Security Bulletin
Summary
Multiple vulnerabilities in the curl/libcurl are related to unauthorized access.
Vulnerability Details
CVEID: CVE-2026-1965
DESCRIPTION: libcurl can in some circumstances reuse the wrong connection when asked to do
an Negotiate-authenticated HTTP or HTTPS request.
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 criterion must first 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. One underlying reason being that
Negotiate sometimes authenticates *connections* and not *requests*, contrary
to how HTTP is designed to work.
An application that allows Negotiate authentication to a server (that responds
wanting Negotiate) with `user1:password1` and then does another operation to
the same server also using Negotiate but with `user2:password2` (while the
previous connection is still alive) - the second request wrongly reused the
same connection and since it then sees that the Negotiate negotiation is
already made, it just sends the request over that connection thinking it uses
the user2 credentials when it is in fact still using the connection
authenticated for user1...
The set of authentication methods to use is set with `CURLOPT_HTTPAUTH`.
Applications can disable libcurl's reuse of connections and thus mitigate this
problem, by using one of the following libcurl options to alter how
connections are or are not reused: `CURLOPT_FRESH_CONNECT`,
`CURLOPT_MAXCONNECTS` and `CURLMOPT_MAX_HOST_CONNECTIONS` (if using the
curl_multi API).
CWE: CWE-305: Authentication Bypass by Primary Weakness
CVSS Source: CISA ADP
CVSS Base score: 6.5
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N)
CVEID: CVE-2026-3783
DESCRIPTION: When an OAuth2 bearer token is used for an HTTP(S) transfer, and that transfer
performs a redirect to a second URL, curl could leak that token to the second
hostname under some circumstances.
If the hostname that the first request is redirected to has information in the
used .netrc file, with either of the `machine` or `default` keywords, curl
would pass on the bearer token set for the first host also to the second one.
CWE: CWE-522: Insufficiently Protected Credentials
CVSS Source: CISA ADP
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)
CVEID: CVE-2026-3784
DESCRIPTION: curl would wrongly reuse an existing HTTP proxy connection doing CONNECT to a
server, even if the new request uses different credentials for the HTTP proxy.
The proper behavior is to create or use a separate connection.
CWE: CWE-305: Authentication Bypass by Primary Weakness
CVSS Source: CISA ADP
CVSS Base score: 6.5
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| AIX | 7.3 |
The following fileset levels are vulnerable:
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
key_fileset = aix
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
01 Jul 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:
01 July 2026
Initial Publish date:
01 July 2026
UID
ibm17278678