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Security Bulletin: Multiple vulnerabilities impacts AIX due to cURL libcurl.

Security Bulletin


Summary

Multiple vulnerabilities in the curl/libcurl are related to reuse existing unencrypted connection (CVE-2026-4873), credentials leakage (CVE-2026-6253, CVE-2026-6429, CVE-2026-7168), cookies leakage(CVE-2026-6276).

Vulnerability Details

CVEID:   CVE-2026-4873
DESCRIPTION:   A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.
CWE:   CWE-319: Cleartext Transmission of Sensitive Information
CVSS Source:   CISA ADP
CVSS Base score:   5.9
CVSS Vector:   (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVEID:   CVE-2026-6253
DESCRIPTION:   curl might erroneously pass on credentials for a first proxy to a second proxy. This can happen when the following conditions are true: 1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy
CWE:   CWE-522: Insufficiently Protected Credentials
CVSS Source:   CISA ADP
CVSS Base score:   5.9
CVSS Vector:   (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-6276
DESCRIPTION:   Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.
CWE:   CWE-346: Origin Validation Error
CVSS Source:   NVD
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-6429
DESCRIPTION:   When asked to both use a `.netrc` file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.
CWE:   CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
CVSS Source:   CISA ADP
CVSS Base score:   5.3
CVSS Vector:   (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N)

CVEID:   CVE-2026-7168
DESCRIPTION:   Successfully using libcurl to do a transfer over a specific HTTP proxy (`proxyA`) with **Digest** authentication and then changing the proxy host to a second one (`proxyB`) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the `Proxy-Authorization:` header field meant for `proxyA`, to `proxyB`.
CWE:   CWE-294: Authentication Bypass by Capture-replay
CVSS Source:   NVD
CVSS Base score:   5.3
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

Affected Products and Versions

Affected Product(s)Version(s)
AIX7.3

 

The following fileset levels are vulnerable:

key_fileset = aix

FilesetLower LevelUpper LevelKEY
oss.lib.libcurl7.79.1.07.79.1.0key_w_fs
oss.lib.libcurl8.1.2.08.1.2.0key_w_fs
oss.lib.libcurl8.5.0.08.5.0.2key_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/Fixes

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_fix12.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 LevelInterim Fix (*.Z) KEY
 7.3  7168mb.260916.epkg.Zkey_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_fix12.tar

cd curl_fix12

 

Verify you have retrieved the fixes intact:

The checksums below were generated using the following command.

"openssl dgst -sha256 [filename]"

openssl dgst -sha256 filenameKEY
30c72f4ac6a03c83941e982a4370368683fb7479d88b59ec009dc0c391f908fa7168mb.260916.epkg.Z key_w_csum

 

The checksums below were generated using the following command.

"openssl dgst -sha512 [filename]"

openssl dgst -sha512filename KEY
f8a6a68649a8a01e4cf4295ad756c73a2f6184aa81cd18623d8175f172a0d48d2933383ff36407f87c7ecac06c48b2d39bf697e466aa7a47c2eeda803bc185a77168mb.260916.epkg.Zkey_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 integrity 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_advisory12.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

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References

Complete CVSS v3 Guide
On-line Calculator v3

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Related Information

IBM Secure Engineering Web Portal
IBM Product Security Incident Response Blog

Acknowledgement

Change History

21 Sep 2026: Initial Publication

*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. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.

Document Location

Worldwide

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Document Information

Modified date:
21 September 2026

Initial Publish date:
21 September 2026

UID

ibm17288632

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