Exhibit 4.2

SECURITY AGREEMENT:

SPECIFIC RIGHTS TO PAYMENT

1. GRANT OF SECURITY INTEREST. For valuable consideration, the undersigned BARRETT BUSINESS SERVICES, INC., or any of them (“Debtor”), hereby grants and transfers to WELLS FARGO BANK, NATIONAL ASSOCIATION (“Bank”) a security interest in the following accounts, deposit accounts, chattel paper (whether electronic or tangible), instruments, promissory notes, documents, general intangibles, payment intangibles, software, letter of credit rights, health-care insurance receivables and other rights to payment (collectively called “Collateral”):

deposit account number 1292505821 at Bank (whether held in Borrower’s name or as a Bank collateral account for the benefit of Borrower, any sub-account thereunder or consolidated therewith, and all renewals, replacements or substitutions therefore, including any account resulting from a renumbering or other administrative re-identification thereof, the “Account”) and all amounts from time to time on deposit in the Account and all interest thereon;

and all renewals thereof, including all securities, guaranties, warranties, indemnity agreements, insurance policies, supporting obligations and other agreements pertaining to the same or the property described therein, together with whatever is receivable or received when any of the Collateral or proceeds thereof are sold, collected, exchanged or otherwise disposed of, whether such disposition is voluntary or involuntary, including without limitation, all rights to payment, including returned premiums, with respect to any insurance relating to any of the foregoing, and all rights to payment with respect to any claim or cause of action affecting or relating to any of the foregoing (hereinafter called “Proceeds”).

2. OBLIGATIONS SECURED. The obligations secured hereby are the payment and performance of: (a) all present and future Indebtedness of Debtor to Bank arising under or in connection with Irrevocable Standby Letter of Credit No. IS0013451 in the amount of Sixty Three Million Nine Hundred Forty Three Thousand Eight Hundred Thirty Two and 00/100 Dollars ($63,943,832.00) and all extensions, renewals or modifications thereof, and restatements or substitutions therefore (the “Letter of Credit”) issued pursuant to the terms of that certain Standby Letter of Credit Agreement (Credit Agreement/Loan Agreement Version) between Borrower and Bank dated September 18, 2012, as may be amended from time to time; and (b) all obligations of Debtor and rights of Bank under this Agreement. The word “Indebtedness” is used herein in its most comprehensive sense and includes any and all advances, debts, obligations and liabilities of Debtor, or any of them, heretofore, now or hereafter made, incurred or created, whether voluntary or involuntary and however arising, whether due or not due, absolute or contingent, liquidated or unliquidated, determined or undetermined, including under any swap, derivative, foreign exchange, hedge, deposit, treasury management or other similar transaction or arrangement, and whether Debtor may be liable individually or jointly with others, or whether recovery upon such Indebtedness may be or hereafter becomes unenforceable.

3. CONTROL OF THE ACCOUNT. As of and after the date of this Agreement, Owner may not make debits to or withdrawals from the Account and Owner shall have no access to the Account or to funds at any time on deposit in the Account. Bank shall have the exclusive access to the Account and to funds at any time on deposit in the Account; provided, however, that so long as no Event of Default has occurred, Bank shall pay interest on the funds on deposit in the Account quarterly in arrears at the interest rate applicable to time deposits as determined by Bank from time in its sole discretion.

4. TERMINATION. This Agreement will terminate upon the performance of all obligations of Debtor to Bank with respect to the Letter of Credit, including without limitation, the payment of all Indebtedness of Debtor to Bank with respect to the Letter of Credit, and the termination of all commitments of Bank to extend credit to Debtor with respect to the Letter of Credit, existing at the time Bank receives written notice from Debtor of the termination of this Agreement.

5. OBLIGATIONS OF BANK. Bank has no obligation to make any loans hereunder. Any money received by Bank in respect of the Collateral may be deposited, at Bank’s option, into a non-interest bearing account over which Debtor shall have no control, and the same shall, for all purposes, be deemed Collateral hereunder.

6. REPRESENTATIONS AND WARRANTIES. Debtor represents and warrants to Bank that: (a) Debtor’s legal name is exactly as set forth on the first page of this Agreement, and all of Debtor’s organizational documents or agreements delivered to Bank are complete and accurate in every respect; (b) Debtor is the owner and has possession or control of the Collateral and Proceeds; (c) Debtor has the exclusive right to grant a security interest in the Collateral and Proceeds; (d) all Collateral and Proceeds are genuine, free from liens, adverse claims, setoffs, default, prepayment, defenses and conditions precedent of any kind or character, except the lien created hereby or as otherwise agreed to by Bank, or as heretofore disclosed by Debtor to Bank, in writing; (e) all statements contained herein and, where applicable, in the Collateral are true and complete in all material respects; (f) no financing statement covering any of the Collateral or Proceeds, and naming any secured party other than Bank, is on file in any public office; (g) all persons appearing to be obligated on Collateral and Proceeds have authority and capacity to contract and are bound as they appear to be; (h) all property subject to chattel paper has been properly registered and filed in compliance with law and to perfect the interest of Debtor in such property; and (i) all Collateral and Proceeds comply with all applicable laws concerning form, content and manner of preparation and execution, including where applicable Federal Reserve Regulation Z and any State consumer credit laws.

7. COVENANTS OF DEBTOR.

(a) Debtor agrees in general: (i) to pay Indebtedness secured hereby when due; (ii) to indemnify Bank against all losses, claims, demands, liabilities and expenses of every kind caused by property subject hereto; (iii) to permit Bank to exercise its powers; (iv) to execute and deliver such documents as Bank deems necessary to create, perfect and continue the security interests contemplated hereby; (v) not to change its name, and as applicable, its chief executive office, its principal residence or the jurisdiction in which it is organized and/or registered without giving Bank prior written notice thereof; (vi) not to change the places where Debtor keeps any Collateral or Debtor’s records concerning the Collateral and Proceeds without giving Bank prior written notice of the address to which Debtor is moving same; and (vii) to cooperate with Bank in perfecting all security interests granted herein and in obtaining such agreements from third parties as Bank deems necessary, proper or convenient in connection with the preservation, perfection or enforcement of any of its rights hereunder.

(b) Debtor agrees with regard to the Collateral and Proceeds, unless Bank agrees otherwise in writing: (i) that Bank is authorized to file financing statements in the name of Debtor to perfect Bank’s security interest in Collateral and Proceeds; (ii) where applicable, to insure the

Collateral with Bank named as loss payee, in form, substance and amounts, under agreements, against risks and liabilities, and with insurance companies satisfactory to Bank; (iii) not to permit any lien on the Collateral or Proceeds, except in favor of Bank; (iv) not to sell, hypothecate or otherwise dispose of, nor permit the transfer by operation of law of, any of the Collateral or Proceeds or any interest therein, nor withdraw any funds from any deposit account pledged to Bank hereunder; (v) to keep, in accordance with generally accepted accounting principles, complete and accurate records regarding all Collateral and Proceeds, and to permit Bank to inspect the same and make copies thereof at any reasonable time; (vi) if requested by Bank, to receive and use reasonable diligence to collect Proceeds, in trust and as the property of Bank, and to immediately endorse as appropriate and deliver such Proceeds to Bank daily in the exact form in which they are received together with a collection report in form satisfactory to Bank; (vii) not to commingle Collateral or Proceeds, or collections thereunder, with other property; (viii) in the event Bank elects to receive payments of Collateral and Proceeds hereunder, to pay all expenses incurred by Bank in connection therewith, including expenses of accounting, correspondence, collection efforts, reporting to account or contract debtors, filing, recording, record keeping and expenses incidental thereto; and (ix) to provide any service and do any other acts which may be necessary to keep all Collateral and Proceeds free and clear of all defenses, rights of offset and counterclaims.

(c) Debtor agrees that the principal balance of time deposit funds in the Account shall at all times be equal to or greater than Three Million Four Hundred Forty Three Thousand Eight Hundred Thirty Two and 00/100 Dollars ($3,443,832.00) (the “Minimum Collateral Value”). In the event that the time deposit funds in the Account, for any reason and at any time is less than the Minimum Collateral Value, Debtor shall promptly increase the principal amount of the time deposit pledged hereunder in an amount sufficient to achieve the Minimum Collateral Value.

8. POWERS OF BANK. Debtor appoints Bank its true attorney in fact to perform any of the following powers, which are coupled with an interest, are irrevocable until termination of this Agreement and may be exercised from time to time by Bank’s officers and employees, or any of them, whether or not Debtor is in default: (a) to perform any obligation of Debtor hereunder in Debtor’s name or otherwise; (b) to give notice to account debtors or others of Bank’s rights in the Collateral and Proceeds, to enforce or forebear from enforcing the same and make extension or modification agreements with respect thereto; (c) to release persons liable on Collateral or Proceeds and to give receipts and acquittances and compromise disputes in connection therewith; (d) to release or substitute security; (e) to resort to security in any order; (f) to prepare, execute, file, record or deliver notes, assignments, schedules, designation statements, financing statements, continuation statements, termination statements, statements of assignment, applications for registration or like papers to perfect, preserve or release Bank’s interest in the Collateral and Proceeds; (g) to receive, open and read mail addressed to Debtor; (h) to take cash, instruments for the payment of money and other property to which Bank is entitled; (i) to verify facts concerning the Collateral and Proceeds by inquiry of obligors thereon, or otherwise, in its own name or a fictitious name; (j) to endorse, collect, deliver and receive payment under instruments for the payment of money constituting or relating to Proceeds; (k) to prepare, adjust, execute, deliver and receive payment under insurance claims, and to collect and receive payment of and endorse any instrument in payment of loss or returned premiums or any other insurance refund or return, and to apply such amounts received by Bank, at Bank’s sole option, toward repayment of the Indebtedness; (l) to exercise all rights, powers and remedies which Debtor would have, but for this Agreement, with respect to all Collateral and Proceeds subject hereto; (m) to make withdrawals from and to close deposit accounts or other accounts with any financial institution, wherever located, into which Proceeds may have been

deposited, and to apply funds so withdrawn to payment of the Indebtedness; (n) to preserve or release the interest evidenced by chattel paper to which Bank is entitled hereunder and to endorse and deliver any evidence of title incidental thereto; and (o) to do all acts and things and execute all documents in the name of Debtor or otherwise, deemed by Bank as necessary, proper and convenient in connection with the preservation, perfection or enforcement of its rights hereunder.

9. PAYMENT OF PREMIUMS, TAXES, CHARGES, LIENS AND ASSESSMENTS. Debtor agrees to pay, prior to delinquency, all insurance premiums, taxes, charges, liens and assessments against the Collateral and Proceeds, and upon the failure of Debtor to do so, Bank at its option may pay any of them and shall be the sole judge of the legality or validity thereof and the amount necessary to discharge the same. Any such payments made by Bank shall be obligations of Debtor to Bank, due and payable immediately upon demand, together with interest at a rate determined in accordance with the provisions of this Agreement, and shall be secured by the Collateral and Proceeds, subject to all terms and conditions of this Agreement.

10. EVENTS OF DEFAULT. The occurrence of any of the following shall constitute an “Event of Default” under this Agreement: (a) any default in the payment or performance of any obligation, or any defined event of default, under (i) any contract or instrument evidencing any Indebtedness, or (ii) any other agreement between Debtor and Bank, including without limitation any loan agreement, relating to or executed in connection with any Indebtedness; (b) any representation or warranty made by Debtor herein shall prove to be incorrect, false or misleading in any material respect when made; (c) Debtor shall fail to observe or perform any obligation or agreement contained herein; (d) any impairment of the rights of Bank in any Collateral or Proceeds, or any attachment or like levy on any property of Debtor; and (e) Bank, in good faith, believes any or all of the Collateral and/or Proceeds to be in danger of misuse, dissipation, commingling, loss, theft, damage or destruction, or otherwise in jeopardy or unsatisfactory in character or value.

11. REMEDIES. Upon the occurrence of any Event of Default, Bank shall have the right to declare immediately due and payable all or any Indebtedness secured hereby and to terminate any commitments to make loans or otherwise extend credit to Debtor. Bank shall have all other rights, powers, privileges and remedies granted to a secured party upon default under the Oregon Uniform Commercial Code or otherwise provided by law, including without limitation, the right (a) to contact all persons obligated to Debtor on any Collateral or Proceeds and to instruct such persons to deliver all Collateral and/or Proceeds directly to Bank, and (b) to sell, lease, license or otherwise dispose of any or all Collateral. All rights, powers, privileges and remedies of Bank shall be cumulative. No delay, failure or discontinuance of Bank in exercising any right, power, privilege or remedy hereunder shall affect or operate as a waiver of such right, power, privilege or remedy; nor shall any single or partial exercise of any such right, power, privilege or remedy preclude, waive or otherwise affect any other or further exercise thereof or the exercise of any other right, power, privilege or remedy. Any waiver, permit, consent or approval of any kind by Bank of any default hereunder, or any such waiver of any provisions or conditions hereof, must be in writing and shall be effective only to the extent set forth in writing. It is agreed that public or private sales or other dispositions, for cash or on credit, to a wholesaler or retailer or investor, or user of property of the types subject to this Agreement, or public auctions, are all commercially reasonable since differences in the prices generally realized in the different kinds of dispositions are ordinarily offset by the differences in the costs and credit risks of such dispositions. While an Event of Default exists: (a) Debtor will deliver to Bank from time to time, as requested by Bank, current lists of all Collateral and Proceeds; (b) Debtor will not dispose of any Collateral or Proceeds except on terms approved

by Bank; (c) Bank may, at any time and at Bank’s sole option, liquidate any time deposits pledged to Bank hereunder and apply the Proceeds thereof to payment of the Indebtedness, whether or not said time deposits have matured and notwithstanding the fact that such liquidation may give rise to penalties for early withdrawal of funds; and (d) at Bank’s request, Debtor will assemble and deliver all Collateral and Proceeds, and books and records pertaining thereto, to Bank at a reasonably convenient place designated by Bank. Debtor further agrees that Bank shall have no obligation to process or prepare any Collateral for sale or other disposition.

12. DISPOSITION OF COLLATERAL AND PROCEEDS; TRANSFER OF INDEBTEDNESS. In disposing of Collateral hereunder, Bank may disclaim all warranties of title, possession, quiet enjoyment and the like. Any proceeds of any disposition of any Collateral or Proceeds, or any part thereof, may be applied by Bank to the payment of expenses incurred by Bank in connection with the foregoing, including reasonable attorneys’ fees, and the balance of such proceeds may be applied by Bank toward the payment of the Indebtedness in such order of application as Bank may from time to time elect. Upon the transfer of all or any part of the Indebtedness, Bank may transfer all or any part of the Collateral or Proceeds and shall be fully discharged thereafter from all liability and responsibility with respect to any of the foregoing so transferred, and the transferee shall be vested with all rights and powers of Bank hereunder with respect to any of the foregoing so transferred; but with respect to any Collateral or Proceeds not so transferred Bank shall retain all rights, powers, privileges and remedies herein given.

13. STATUTE OF LIMITATIONS. Until all Indebtedness shall have been paid in full and all commitments by Bank to extend credit to Debtor have been terminated, the power of sale or other disposition and all other rights, powers, privileges and remedies granted to Bank hereunder shall continue to exist and may be exercised by Bank at any time and from time to time irrespective of the fact that the Indebtedness or any part thereof may have become barred by any statute of limitations, or that the personal liability of Debtor may have ceased, unless such liability shall have ceased due to the payment in full of all Indebtedness secured hereunder.

14. MISCELLANEOUS. When there is more than one Debtor named herein: (a) the word “Debtor” shall mean all or any one or more of them as the context requires; (b) the obligations of each Debtor hereunder are joint and several; and (c) until all Indebtedness shall have been paid in full, no Debtor shall have any right of subrogation or contribution, and each Debtor hereby waives any benefit of or right to participate in any of the Collateral or Proceeds or any other security now or hereafter held by Bank. Debtor hereby waives any right to require Bank to (i) proceed against Debtor or any other person, (ii) marshal assets or proceed against or exhaust any security from Debtor or any other person, (iii) perform any obligation of Debtor with respect to any Collateral or Proceeds, and (iv) make any presentment or demand, or give any notice of nonpayment or nonperformance, protest, notice of protest or notice of dishonor hereunder or in connection with any Collateral or Proceeds. Debtor further waives any right to direct the application of payments or security for any Indebtedness of Debtor or indebtedness of customers of Debtor.

15. NOTICES. All notices, requests and demands required under this Agreement must be in writing, addressed to Bank at the address specified in any other loan documents entered into between Debtor and Bank and to Debtor at the address of its chief executive office (or principal residence, if applicable) specified below or to such other address as any party may designate by written notice to each other party, and shall be deemed to have been given or

made as follows: (a) if personally delivered, upon delivery; (b) if sent by mail, upon the earlier of the date of receipt or three (3) days after deposit in the U.S. mail, first class and postage prepaid; and (c) if sent by telecopy, upon receipt.

16. COSTS, EXPENSES AND ATTORNEYS’ FEES. Debtor shall pay to Bank immediately upon demand the full amount of all payments, advances, charges, costs and expenses, including reasonable attorneys’ fees (to include outside counsel fees and all allocated costs of Bank’s in-house counsel), expended or incurred by Bank in connection with (a) the perfection and preservation of the Collateral or Bank’s interest therein, and (b) the realization, enforcement and exercise of any right, power, privilege or remedy conferred by this Agreement, whether incurred at the trial or appellate level, in an arbitration proceeding or otherwise, and including any of the foregoing incurred in connection with any bankruptcy proceeding (including without limitation, any adversary proceeding, contested matter or motion brought by Bank or any other person) relating to Debtor or in any way affecting any of the Collateral or Bank’s ability to exercise any of its rights or remedies with respect thereto. All of the foregoing shall be paid by Debtor with interest from the date of demand until paid in full at a rate per annum equal to the greater of ten percent (10%) or Bank’s Prime Rate in effect from time to time.

17. SUCCESSORS; ASSIGNS; AMENDMENT. This Agreement shall be binding upon and inure to the benefit of the heirs, executors, administrators, legal representatives, successors and assigns of the parties, and may be amended or modified only in writing signed by Bank and Debtor.

18. OBLIGATIONS OF MARRIED PERSONS. Any married person who signs this Agreement as Debtor hereby expressly agrees that recourse may be had against his or her separate property for all his or her Indebtedness to Bank secured by the Collateral and Proceeds under this Agreement.

19. SEVERABILITY OF PROVISIONS. If any provision of this Agreement shall be held to be prohibited by or invalid under applicable law, such provision shall be ineffective only to the extent of such prohibition or invalidity, without invalidating the remainder of such provision or any remaining provisions of this Agreement.

20. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the laws of the State of Oregon.

Debtor warrants that Debtor is an organization registered under the laws of Maryland.

Debtor warrants that its chief executive office (or principal residence, if applicable) is located at the following address: 8100 NE Parkway Drive, Suite 200, Vancouver, Washington 98662.

Debtor warrants that the Collateral (except goods in transit) is located or domiciled at the following additional addresses: [Not applicable].

UNDER OREGON LAW, MOST AGREEMENTS, PROMISES AND COMMITMENTS MADE BY BANK CONCERNING LOANS AND OTHER CREDIT EXTENSIONS WHICH ARE NOT FOR PERSONAL, FAMILY OR HOUSEHOLD PURPOSES OR SECURED SOLELY BY THE BORROWER’S RESIDENCE MUST BE IN WRITING, EXPRESS CONSIDERATION AND BE SIGNED BY BANK TO BE ENFORCEABLE.

IN WITNESS WHEREOF, this Agreement has been duly executed as of June 14, 2013.