Unscored severity · published Oct 20, 2026
CVE-2026-86409
stale SigV4 headers sent unintended
–
CVSS
0.3%
EPSS
No
On KEV
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.
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 24% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CU
curl · curl
8.21.0 through 8.21.0; 8.20.0 through 8.20.0; 8.19.0 through 8.19.0; 8.18.0 through 8.18.0; 8.17.0 through 8.17.0; 8.16.0 through 8.16.0; +34 more · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-86409
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-86409
curl.se
https://curl.se/docs/CVE-2026-86409.html
curl.se
https://curl.se/docs/CVE-2026-86409.json
hackerone.com
https://hackerone.com/reports/3973135
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