Security Bulletin
Summary
A logic error allows libcurl to reuse an existing Negotiate-authenticated connection even when a new request specifies different credentials for the same server.
Vulnerability Details
CVEID: CVE-2026-5545
DESCRIPTION: libcurl might in some circumstances reuse the wrong connection when asked to
do an authenticated HTTP(S) request after a Negotiate-authenticated one, when
both use the same host.
libcurl features a pool of recent connections so that subsequent requests can
reuse an existing connection to avoid overhead.
When reusing a connection a range of criteria must be met. Due to a logical
error in the code, a request that was issued by an application could
wrongfully reuse an existing connection to the same server that was
authenticated using different credentials.
An application that first uses Negotiate authentication to a server with
`user1:password1` and then does another operation to the same server asking
for any authentication method but for `user2:password2` (while the previous
connection is still alive) - the second request gets confused and wrongly
reuses the same connection and sends the new request over that connection
thinking it uses a mix of user1's and user2's credentials when it is in fact
still using the connection authenticated for user1...
CWE: CWE-613: Insufficient Session Expiration
CVSS Source: NVD
CVSS Base score: 6.5
CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| 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/Fixes
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_fix10.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 3784ma.260518.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_fix10.tar
cd curl_fix10
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
-----------------------------------------------------------------------------------------------------
1554c73f9f181291b515225a96c2f241488d513a73fa1419182fb5b33b4a6c47 3784ma.260518.epkg.Z key_w_csum
The checksums below were generated using the
"openssl dgst -sha512 [filename]" command as the following:
openssl dgst -sha512 filename
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
817030720de4e128685e6f4dde802d6b448499d61505216765797d5fec38cdce93d288fed1a9a7942586d5e72bf296f748862659cb19329b71d917718dd58cb2 3784ma.260518.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 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_advisory10.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
Get Notified about Future Security Bulletins
References
Acknowledgement
Change History
30 Jun 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:
30 June 2026
Initial Publish date:
30 June 2026
UID
ibm17278558