# CVE-2026-87866: curl wolfSSL public-key pinning bypass

Source: https://junglewise.ai/threats/cve-2026-87866-when-built-with-wolfssl-curl-can-successfully-validate-a-pinned  
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-2026-87866 · Severity: info · Published 2026-10-20

curl, a widely used tool for transferring data over the internet, can be tricked into accepting fraudulent TLS certificates when built with the wolfSSL library. An attacker can create a specially malformed certificate that passes wolfSSL's initial validation but exploits a parsing bug in curl to bypass public-key pinning checks, allowing man-in-the-middle attacks to intercept secure connections. This affects applications using libcurl with wolfSSL, not the curl command-line tool itself.

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

## Quick answers

**Is CVE-2026-87866 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-87866 being exploited in the wild.

**How severe is CVE-2026-87866?** Informational severity, published 20 October 2026.

**Which products and versions are affected?** Curl 7.43.0 to 8.22.0 (fixed in 8.14.3, 8.16.2, 8.20.2, 8.23.0 depending on branch).

**Is there a fix for CVE-2026-87866?** Yes: fixed in curl 8.23.0, 8.20.2 (8.20.X branch), 8.16.2 (8.16.X branch), 8.14.3 (8.14.X branch). Until then: Upgrade to a patched curl version. Alternatively, disable public-key pinning or build curl with a different TLS backend instead of wolfSSL. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-87866 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-87866?** 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 8.23.0, 8.20.2 (8.20.X branch), 8.16.2 (8.16.X branch), 8.14.3 (8.14.X branch)

Upgrade to a patched curl version. Alternatively, disable public-key pinning or build curl with a different TLS backend instead of wolfSSL.

## Technical details

The vulnerability is a certificate validation bypass (CWE-295) that occurs when curl is built with wolfSSL as the TLS backend. During TLS handshake, wolfSSL validates a malformed certificate, but curl's subsequent re-parsing of the same certificate using a manipulated validity length field extracts a different embedded key, causing curl's public-key pinning check to match against an attacker-controlled key rather than the legitimate peer key. The attack requires the attacker to present a specifically crafted malformed certificate that wolfSSL accepts but curl misparsed.

## Affected products

- curl curl 7.43.0 to 8.22.0 (fixed in 8.14.3, 8.16.2, 8.20.2, 8.23.0 depending on branch)

## Timeline

- 2026-10-14: disclosed
- 2026-10-14: patched: curl 8.23.0 released coordinated with advisory

## References

- [https://curl.se/docs/CVE-2026-87866.html](https://curl.se/docs/CVE-2026-87866.html)
- [https://curl.se/docs/CVE-2026-87866.json](https://curl.se/docs/CVE-2026-87866.json)

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