CVE-2026-63388: Libevent: Heap out-of-bounds write in bufferevent_socket_set_conn_address_ reachable via AF_UNIX accept

highCVSS 8.4CVE-2026-63388

CSIRTS triage

vendor: Libevent product: Libevent Memory corruption

What: Libevent contains a heap out-of-bounds write in bufferevent_socket_set_conn_address_ triggered via AF_UNIX accept operations.
Who is affected: Applications using Libevent with AF_UNIX sockets and local attack vectors.
Urgency: High severity (CVSS 8.4) and not exploited; prioritize patching to prevent local privilege escalation.
Action: Update Libevent to a version that correctly bounds-checks connection address buffers in AF_UNIX socket handling.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 8.4
Published: 2026-08-11
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63388

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-633880.14% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 4% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-63388	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

highCVE-2026-63388: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a hea…nvd

Recent advisories for Libevent

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-63495: Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libeven…nvd · 2026-08-20
highCVE-2026-63388: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a hea…nvd · 2026-08-20
highCVE-2026-63387: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an of…nvd · 2026-08-20
unknownCVE-2026-63385: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has two H…nvd · 2026-08-20
unknownCVE-2026-63384: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an in…nvd · 2026-08-20
unknownCVE-2026-63383: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent can read …nvd · 2026-08-20