IBM SECURITY ADVISORY First Issued: Tue Jul 28 05:27:04 CDT 2026 The most recent version of this document is available here: https://aix.software.ibm.com/aix/efixes/security/curl_advisory11.asc Security Bulletin: Multiple vulnerabilities impacts AIX due to cURL libcurl (CVE-2026-10536, CVE-2026-11856, CVE-2026-8286, CVE-2026-8458, CVE-2026-8924, CVE-2026-8927, CVE-2026-8932, CVE-2026-9547). =============================================================================== SUMMARY: Multiple vulnerabilities in the curl/libcurl are related to use-after-free, reusing an invalid connection, bypass Public Suffix List checks, improper host key validation and invalid authorization. =============================================================================== VULNERABILITY DETAILS: CVEID: CVE-2026-10536 https://www.cve.org/CVERecord?id=CVE-2026-10536 DESCRIPTION: A use-after-free vulnerability exists in libcurl when an application configures an HTTP/2 stream-dependency tree via `CURLOPT_STREAM_DEPENDS` or `CURLOPT_STREAM_DEPENDS_E`, subsequently invokes `curl_easy_reset()`, and finally terminates the handle with `curl_easy_cleanup()`. During the final cleanup phase, libcurl accesses and modifies an internal structure that was already freed during the reset operation. CVSS Base Score: 9.8 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) CVEID: CVE-2026-11856 https://www.cve.org/CVERecord?id=CVE-2026-11856 DESCRIPTION: After successfully performing a transfer to one HTTP origin (`hostA`) using Digest authentication, reusing the same handle for a second transfer to a different origin (`hostB`) can cause libcurl to incorrectly forward the `Authorization:` header intended for `hostA` to `hostB`. CVSS Base Score: 9.8 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) CVEID: CVE-2026-8286 https://www.cve.org/CVERecord?id=CVE-2026-8286 DESCRIPTION: A vulnerability exists where a new transfer using STARTTLS to upgrade a connection might incorrectly reuse an existing live connection even when the TLS configuration does not match and the connection should not be reused. CVSS Base Score: 8.1 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N) CVEID: CVE-2026-8458 https://www.cve.org/CVERecord?id=CVE-2026-8458 DESCRIPTION: libcurl may incorrectly reuse an existing connection for Negotiate-authenticated requests even when different services are specified. Due to a logical error in the connection reuse logic, a request can reuse a connection previously authenticated for a different service on the same server, potentially resulting in incorrect authentication behavior. CVSS Base Score: 6.5 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N) CVEID: CVE-2026-8924 https://www.cve.org/CVERecord?id=CVE-2026-8924 DESCRIPTION: A flaw in curl's cookie parsing logic allows a malicious HTTP server to set "super cookies" that bypass the Public Suffix List (PSL) check. This enables an attacker-controlled origin to inject cookies that curl subsequently scopes and transmits to unrelated third-party domains. CVSS Base Score: 9.1 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N) CVEID: CVE-2026-8927 https://www.cve.org/CVERecord?id=CVE-2026-8927 DESCRIPTION: When reusing a libcurl handle for sequential transfers driven by environment-variable proxy configuration, libcurl fails to clear the proxy authentication state between requests. If the initial transfer authenticates against `proxyA` using Digest authentication, a subsequent transfer routed through `proxyB` may incorrectly leak the `Proxy-Authorization:` header intended only for `proxyA`. CVSS Base Score: 9.1 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N) CVEID: CVE-2026-8932 https://www.cve.org/CVERecord?id=CVE-2026-8932 DESCRIPTION: libcurl may reuse a previously established connection even after mTLS-related configuration options have changed in a way that should prevent reuse. Some TLS settings related to client certificates, particularly private key options, were omitted from the connection configuration matching logic, allowing inappropriate connection reuse. CVSS Base Score: 7.5 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) CVEID: CVE-2026-9547 https://www.cve.org/CVERecord?id=CVE-2026-9547 DESCRIPTION: When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and uses the `CURLOPT_SSH_KEYFUNCTION` callback, it may silently accept an untrusted server. If the server presents a host key type that differs from the one already recorded in the `known_hosts` file, the callback fails to enforce the expected rejection, allowing the connection to proceed and increasing the risk of a man-in-the-middle attack. CVSS Base Score: 7.4 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N) AFFECTED PRODUCTS AND VERSIONS: AIX 7.3 The following fileset levels are vulnerable: key_fileset = aix Fileset Lower Level Upper Level KEY --------------------------------------------------------- oss.lib.libcurl 7.79.1.0 7.79.1.0 key_w_fs oss.lib.libcurl 8.1.2.0 8.1.2.0 key_w_fs oss.lib.libcurl 8.5.0.0 8.5.0.2 key_w_fs Note: This bulletin does not apply to versions of curl installed from the AIX Toolbox. To find out whether the affected filesets are installed on your systems, refer to the lslpp command found in AIX user's guide. Example: lslpp -L | grep -i oss.lib.libcurl REMEDIATION: A. FIXES IBM strongly recommends addressing the vulnerability now. AIX fixes are available. The AIX fixes can be downloaded via https from: https://aix.software.ibm.com/aix/efixes/security/curl_fix11.tar The link above is to a tar file containing this signed advisory, fix packages, and OpenSSL signatures for each package. The fixes below include prerequisite checking. This will enforce the correct mapping between the fixes and AIX Technology Levels. Note that the tar file contains Interim fixes that are based on Curl version, and AIX Curl fixes are cumulative. AIX Level Interim Fix (*.Z) KEY -------------------------------------------------- 7.3 10536ma.260722.epkg.Z key_w_fix Please reference the Affected Products and Version section above for help with checking installed fileset levels. To extract the fixes from the tar file: tar xvf curl_fix11.tar cd curl_fix11 Verify you have retrieved the fixes intact: The checksums below were generated using the "openssl dgst -sha256 [filename]" command as the following: openssl dgst -sha256 filename KEY ----------------------------------------------------------------------------------------------------- 8136ae524138755586635ca6e8c1367e049c307d617f2d531a815d4f767e3a1b 10536ma.260722.epkg.Z key_w_csum The checksums below were generated using the "openssl dgst -sha512 [filename]" command as the following: openssl dgst -sha512 filename KEY ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 2d2d7fe68db5d5f4935eb269478ac56f6e2b5d11154db6593e458657045e8829c0908786ee8cc08f60eb11a64ed181110f0092f0542ffff397d642b852d57541 10536ma.260722.epkg.Z key_4K_w_csum These sums should match exactly. The OpenSSL signatures in the tar file and on this advisory can also be used to verify the integrityi of the fixes. If the sums or signatures cannot be confirmed, contact IBM Support at http://ibm.com/support/ and describe the discrepancy. openssl dgst -sha256 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file] openssl dgst -sha256 -verify [pubkey_file] -signature [ifix_file].sig [ifix_file] Published advisory OpenSSL signature file location: https://aix.software.ibm.com/aix/efixes/security/curl_advisory11.asc.sig B. FIX AND INTERIM FIX INSTALLATION If possible, it is recommended that a mksysb backup of the system be created. Verify it is both bootable and readable before proceeding. To preview a fix installation: installp -a -d fix_name -p all # where fix_name is the name of the # fix package being previewed. To install a fix package: installp -a -d fix_name -X all # where fix_name is the name of the # fix package being installed. Interim fixes have had limited functional and regression testing but not the full regression testing that takes place for Service Packs; however, IBM does fully support them. Interim fix management documentation can be found at: https://www.ibm.com/support/pages/managing-interim-fixes-aix To preview an interim fix installation: emgr -e ipkg_name -p # where ipkg_name is the name of the # interim fix package being previewed. To install an interim fix package: emgr -e ipkg_name -X # where ipkg_name is the name of the # interim fix package being installed. WORKAROUNDS AND MITIGATIONS: None. =============================================================================== CONTACT US: Note: Keywords labeled as KEY in this document are used for parsing purposes. If you would like to receive AIX Security Advisories via email, please visit "My Notifications": http://www.ibm.com/support/mynotifications Contact IBM Support for questions related to this announcement: https://ibm.com/support/ For information on how to securely verify AIX security bulletins and fixes: https://www.ibm.com/support/pages/node/6985269 To obtain the OpenSSL public key that can be used to verify the signed advisories and ifixes: Download the key from our web page: https://aix.software.ibm.com/aix/efixes/security/systems_p_os_aix_security_pubkey.txt To verify the AIX/VIOS security bulletin: Published advisory OpenSSL signature file location: https://aix.software.ibm.com/aix/efixes/security/curl_advisory11.asc.sig openssl dgst -sha256 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file] Please contact your local IBM AIX support center for any assistance. REFERENCES: Complete CVSS v3 Guide: http://www.first.org/cvss/user-guide On-line Calculator v3: http://www.first.org/cvss/calculator/3.0 RELATED INFORMATION: IBM Secure Engineering Web Portal http://www.ibm.com/security/secure-engineering/bulletins.html IBM Product Security Incident Response Blog https://www.ibm.com/blogs/psirt/ Security Bulletin: https://www.ibm.com/support/pages/node/ ACKNOWLEDGEMENTS: None. CHANGE HISTORY: First Issued: Tue Jul 28 05:27:04 CDT 2026 =============================================================================== *The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin. Disclaimer According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES "AS IS" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY.