# CVE-2026-63388: Libevent heap out-of-bounds write in bufferevent_sock

Source: https://junglewise.ai/threats/cve-2026-63388-libevent-heap-out-of-bounds-write-in-bufferevent-sock  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-20. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-63388 · Severity: high · CVSS 8.4 · Published 2026-08-20

Libevent is an event notification library used by many applications to handle network I/O and timers. A local attacker able to connect to an AF_UNIX socket can craft a malicious peer address that overflows a heap buffer in the library, corrupting adjacent memory. This could allow an attacker to crash the application, read sensitive data from memory, or potentially execute arbitrary code.

Technologies: [Libevent](https://junglewise.ai/threats/technologies/libevent). Vendors: [Libevent](https://junglewise.ai/threats/vendors/libevent).

## Quick answers

**Is CVE-2026-63388 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63388 being exploited in the wild.

**How severe is CVE-2026-63388?** High severity, with a CVSS score of 8.4, published 20 August 2026.

**Which products and versions are affected?** Libevent prior to 2.1.13 and prior to 2.2.2-alpha.

**Is there a fix for CVE-2026-63388?** A patch was published on 2026-08-20: Fixed in versions 2.1.13 and 2.2.2-alpha Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63388 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-63388?** Check whether you run Libevent 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.

## Technical details

The vulnerability is a heap out-of-bounds write (CWE-122) in bufferevent_socket_set_conn_address_ in bufferevent_sock.c. When an AF_UNIX socket connection is accepted by an evhttp server compiled with NDEBUG (which disables assertions), the kernel-supplied peer address (up to 110 bytes) is copied into a 28-byte field without proper length validation. The EVUTIL_ASSERT guard that would catch this is disabled in release builds. An unauthenticated local peer connecting to the AF_UNIX listener can trigger the overflow, overwriting the adjacent dns_request pointer and other heap data. The fix unconditionally validates address length and allocates sufficient storage for AF_UNIX addresses. Patches are available in libevent 2.1.13 and 2.2.2-alpha.

## Affected products

- Libevent Libevent prior to 2.1.13 and prior to 2.2.2-alpha

## Timeline

- 2026-08-20: disclosed
- 2026-08-20: patched: Fixed in versions 2.1.13 and 2.2.2-alpha

## References

- [https://github.com/libevent/libevent/commit/52057cb33d0c20c0a0453fbabe6c0c96854931b9](https://github.com/libevent/libevent/commit/52057cb33d0c20c0a0453fbabe6c0c96854931b9)
- [https://github.com/libevent/libevent/commit/ef38f926e9cd1f082416c6fff13587bc1f431d72](https://github.com/libevent/libevent/commit/ef38f926e9cd1f082416c6fff13587bc1f431d72)

## Related threats

- [Libevent WebSocket unbounded memory accumulation via frame fragmentation](https://junglewise.ai/threats/cve-2026-63495-libevent-websocket-unbounded-memory-accumulation-via-frame)
- [Libevent off-by-one stack buffer overflow in DNS response parsing](https://junglewise.ai/threats/cve-2026-63387-libevent-off-by-one-stack-buffer-overflow-in-dns-response-parsing)
- [Libevent integer overflow in evtag_unmarshal_header](https://junglewise.ai/threats/cve-2026-63384-libevent-integer-overflow-in-evtag-unmarshal-header)
- [Libevent out-of-bounds read in event_tagging](https://junglewise.ai/threats/cve-2026-63383-libevent-out-of-bounds-read-in-event-tagging)
- [Libevent HTTP request smuggling via inconsistent Transfer-Encoding parsing](https://junglewise.ai/threats/cve-2026-63382-libevent-http-request-smuggling-via-inconsistent-transfer)