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CVE-2026-5545

MEDIUMCVSS 6.5/10EPSS 0.41%

Last modified

CVE-2026-5545 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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.... EPSS estimates a 0.41% chance of exploitation in the next 30 days.

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...

Metrics

CVSS 3.1
6.5/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N

EPSS Probability
0.41%

33.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
HaxxCurl>= 7.10.6, < 8.20.0

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-5545?
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...
How severe is CVE-2026-5545?
CVE-2026-5545 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.41% probability of exploitation in the next 30 days.
How do I fix CVE-2026-5545?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-5545?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST