# CVE-2026-63383: Libevent out-of-bounds read in event_tagging

Source: https://junglewise.ai/threats/cve-2026-63383-libevent-out-of-bounds-read-in-event-tagging  
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-2026-63383 · Severity: info · Published 2026-08-20

Libevent is a widely-used event notification library that powers many networked applications and services. A flaw in its RPC tag-decoding logic allows an attacker to send a malformed message that causes the library to read memory beyond its intended bounds. This can crash applications that process untrusted RPC data, resulting in denial of service.

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

## Quick answers

**Is CVE-2026-63383 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63383 being exploited in the wild.

**How severe is CVE-2026-63383?** Informational severity, 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-2026-63383?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-63383 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-63383?** 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 an out-of-bounds read in the decode_tag_internal function in event_tagging.c. The function calls evbuffer_pullup with a calculated window size (at most 6 bytes) but then iterates over the full logical buffer length, causing it to read past the pullup boundary. A fragmented evbuffer containing a six-byte malformed tag can trigger out-of-bounds memory access. The attack vector is network-based: an attacker sends a specially crafted RPC message to a service using Libevent. The fix, applied in versions 2.1.13 and 2.2.2-alpha, constrains the iteration to the actual pullup length.

## Affected products

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

## Timeline

- 2026-08-20: disclosed

## References

- [https://github.com/libevent/libevent/commit/91ed8745eebabdd27592a83d350338a8c4626321](https://github.com/libevent/libevent/commit/91ed8745eebabdd27592a83d350338a8c4626321)
- [https://github.com/libevent/libevent/commit/e1f9e21887c6b104e206a718385ba3ffc75180cb](https://github.com/libevent/libevent/commit/e1f9e21887c6b104e206a718385ba3ffc75180cb)

## 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 heap out-of-bounds write in bufferevent_sock](https://junglewise.ai/threats/cve-2026-63388-libevent-heap-out-of-bounds-write-in-bufferevent-sock)
- [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 HTTP request smuggling via inconsistent Transfer-Encoding parsing](https://junglewise.ai/threats/cve-2026-63382-libevent-http-request-smuggling-via-inconsistent-transfer)