CVE-2026-86409: curl · Setting CURLOPT_AWS_SIGV4 to NULL but does not disable SigV4 authentication, contrary to expectations
Affects curlSource GCVE Database
Not known to be exploited · fixed in 7.81.0-1ubuntu1.30 : patch curl soon.
Data as of 28 Oct 2026, 22:28 UTC
Rated by Threat Radar · CVSS not yet scored by NVD
- Patch
- Available – fixed in 7.81.0-1ubuntu1.30, 8.5.0-2ubuntu10.16, 8.20.0-2ubuntu11.1 +1
Exploitation evidence
Disclosed: evidence found.
CVE published 20 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Patches and advisories
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10curlpkg:deb/ubuntu/curl?arch=source&distro=stonkingOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTScurlpkg:deb/ubuntu/curl?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTScurlpkg:deb/ubuntu/curl?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 22.04 LTScurlpkg:deb/ubuntu/curl?arch=source&distro=jammyOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
Setting `CURLOPT_AWS_SIGV4` to NULL but does not disable SigV4 authentication, contrary to expectations and documentation. A subsequent transfer on the same handle still sends an `Authorization: AWS4-HMAC-SHA256` header to whatever URL isset next, leaking state information.
References
- ubuntu.com/security/CVE-2026-86409 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-86409 (opens in a new tab)
- curl.se/docs/CVE-2026-86409.html (opens in a new tab)
- ubuntu.com/security/notices/USN-8927-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8927-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8932-1 (opens in a new tab)