CVE-2026-5545
MEDIUMDescription
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 to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N/E:U
Exploit Intelligence
Low risk: more likely to be exploited than 35% of all known CVEs.
References
Related Vulnerabilities
Other CWE-305 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-31161 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2020-10923 | High | 8.8 | 85% | - | - |
| CVE-2023-28126 | Medium | 5.9 | 67% | - | - |
| CVE-2023-34124 | Critical | 9.8 | 50% | - | Fix |
| CVE-2025-32011 | Critical | 9.8 | 27% | - | - |
| CVE-2024-37085 | Medium | 6.8 | 27% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2026-5545?
Published advisories record a fix for 13 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2026-5545 being actively exploited?
Not that we know of. CVE-2026-5545 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.41% is the estimated probability that it will be exploited in the next 30 days. That is higher than 35% of all scored CVEs.
How severe is CVE-2026-5545?
CVE-2026-5545 has a CVSS v3 base score of 6.5, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-5545 affect?
Published advisories record a fix for curl (Debian), curl (Red Hat / RHEL), curl (Rocky), curl (Ubuntu), and 9 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-15.