CVE-2026-63383 Libevent: decode_tag_internal() can lead to out-of-bounds read
An out-of-bounds read in Libevent's RPC decoding allows attackers to crash applications processing malformed tagged data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63383?
CVE-2026-63383 is a high-severity memory corruption vulnerability in libevent, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-125
Which versions are affected by CVE-2026-63383?
How do I fix CVE-2026-63383?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-63383 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63383 exists.
Sources
Also known as AZL-96921, AZL-96938, AZL-97521, AZL-97551, BELL-CVE-2026-63383, DEBIAN-CVE-2026-63383 and 4 more.