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Fencer Intel
high 7.5

CVE-2026-63495 json

Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames

published 4mo ago modified 16d ago also EUVD-2026-63503 , GHSA-qx89-wf2v-vgmx

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository libevent/libevent. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.

Patch / fix

  • libevent_project libevent 2.2.2-alpha
  • libevent hummingbird 1 2.1.12-19.hum1

red hat advisories RHSA-2026:41176

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-63495 updated cvss 7.5

libevent: Libevent: Remote denial of service via unbounded memory accumulation in WebSocket server

  • Red Hat Enterprise Linux 6 libevent2 2.0.21-2.el6
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Hardened Images libevent 2.1.12-19.hum1
    fixed: vendor fix RHSA-2026:41176
  • Red Hat Enterprise Linux 6 libevent 2.1.12-16.el10 Red Hat Enterprise Linux 7 libevent 2.1.12-16.el10 Red Hat Enterprise Linux 8 libevent, libevent 2.1.12-16.el10 Red Hat Enterprise Linux 9 libevent, libevent 2.1.12-16.el10 Red Hat Enterprise Linux 10 libevent 2.1.12-16.el10
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
2mo ago

Exploit prediction

0.61% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/libevent/libevent/security/advisories/GHSA-qx89-wf2v-vgmx referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • libevent libevent

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of libevent/libevent published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.