Vulnerability · Published Oct 20, 2026 · Assigned by curl
CVE-2026-86409stale SigV4 headers sent unintended
High 8.1
In plain English
A high-severity security flaw in curl from curl. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.1% (higher than 66% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)8.1High
Exploit odds (30 days)1.1%top 34.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | curl | 8.23.0-r0 | ALPINE-CVE-2026-86409 |
| Alpine:v3.24 | curl | 8.23.0-r0 | ALPINE-CVE-2026-86409 |
| Debian:12 | curl | no fix listed | DEBIAN-CVE-2026-86409 |
| Debian:13 | curl | no fix listed | DEBIAN-CVE-2026-86409 |
| Debian:14 | curl | 8.22.0-1 | DEBIAN-CVE-2026-86409 |
| Ubuntu:22.04:LTS | curl | 7.81.0-1ubuntu1.30 | USN-8932-1 |
| Ubuntu:22.04:LTS | curl | 7.81.0-1ubuntu1.30 | UBUNTU-CVE-2026-86409 |
| Ubuntu:24.04:LTS | curl | 8.5.0-2ubuntu10.16 | USN-8932-1 |
| Ubuntu:24.04:LTS | curl | 8.5.0-2ubuntu10.16 | UBUNTU-CVE-2026-86409 |
| Ubuntu:26.04:LTS | curl | 8.18.0-1ubuntu2.8 | USN-8927-1 |
| Ubuntu:26.04:LTS | curl | 8.18.0-1ubuntu2.8 | UBUNTU-CVE-2026-86409 |
| Ubuntu:26.10 | curl | 8.20.0-2ubuntu11.1 | USN-8927-2 |
| Ubuntu:26.10 | curl | 8.20.0-2ubuntu11.1 | UBUNTU-CVE-2026-86409 |
Affected products (as reported)
Weakness: CWE-201 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H