# CVE-2026-86409: curl stale SigV4 headers sent unintended

Source: https://junglewise.ai/threats/cve-2026-86409-setting-curlopt-aws-sigv4-to-null-but-does-not-disable-sigv4  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-86409 · Severity: info · Published 2026-10-20

curl is a widely-used library and command-line tool for transferring data with URLs. When an application reuses a curl connection handle after attempting to disable AWS SigV4 authentication, the library incorrectly continues to send signed Authorization headers to subsequent requests, potentially leaking the access-key identifier and cryptographic signature to an attacker-controlled server.

Technologies: [Curl](https://junglewise.ai/threats/technologies/curl-curl). Vendors: [Curl](https://junglewise.ai/threats/vendors/curl).

## Quick answers

**Is CVE-2026-86409 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86409 being exploited in the wild.

**How severe is CVE-2026-86409?** Informational severity, published 20 October 2026.

**Which products and versions are affected?** Curl 7.75.0 to 8.21.0 (except 8.14.3, 8.16.2, 8.20.2).

**Is there a fix for CVE-2026-86409?** Yes: fixed in curl 8.22.0, 8.20.2 (8.20.x branch), 8.16.2 (8.16.x branch), 8.14.3 (8.14.x branch). Until then: Do not attempt to NULL the CURLOPT_AWS_SIGV4 option when reusing handles; instead, create a fresh handle for requests that should not use SigV4 authentication. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86409 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-86409?** Check whether you run Curl at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in curl 8.22.0, 8.20.2 (8.20.x branch), 8.16.2 (8.16.x branch), 8.14.3 (8.14.x branch)

Do not attempt to NULL the CURLOPT_AWS_SIGV4 option when reusing handles; instead, create a fresh handle for requests that should not use SigV4 authentication.

## Technical details

Setting CURLOPT_AWS_SIGV4 to NULL fails to disable SigV4 authentication; subsequent transfers on the same handle still send AWS4-HMAC-SHA256 Authorization headers, contrary to documented behavior. The vulnerability requires an application that reuses handles, retains USERPWD credentials, relies on the NULL reset mechanism, and issues a request to an attacker-influenced URL. An attacker gains the access-key identifier and request-bound signature (but not the secret key); this is classified as information exposure through sent data (CWE-201).

## Affected products

- curl curl 7.75.0 to 8.21.0 (except 8.14.3, 8.16.2, 8.20.2)

## Timeline

- 2026-08-27: disclosed
- 2026-09-02: patched
- 2026-10-14: advisory

## References

- [https://curl.se/docs/CVE-2026-86409.html](https://curl.se/docs/CVE-2026-86409.html)
- [https://curl.se/docs/CVE-2026-86409.json](https://curl.se/docs/CVE-2026-86409.json)

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