What is CVE-2021-40516?

CVE-2021-40516 is a high-severity vulnerability in Weechat, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2021-09-05.

How severe is CVE-2021-40516?

High severity. CVSS v3 base score is 7.5 out of 10.

Out-of-bounds Read in Weechat

CVE-2021-40516

WeeChat before 3.2.1 allows remote attackers to cause a denial of service (crash) via a crafted WebSocket frame that trigger an out-of-bounds read in plugins/relay/relay-websocket.c in the Relay plugin.

Vulnerability class: Buffer Overflow

Published 2021-09-05 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.016 (74.9th percentile), scored 2026-10-07.

Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 74.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: 0.000

Affected products

Weechat
Debian Linux — versions 10.0

Weakness classification (CWE)

CWE-125 — Out-of-bounds Read

References

weechat.org/doc/security/ (Patch, Vendor Advisory)
github.com/weechat/weechat/commit/8b1331f98de1714bae15a9ca2e2b393ba49d735b (Patch, Third Party Advisory)
lists.debian.org/debian-lts-announce/2021/09/msg00018.html (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-40516?: CVE-2021-40516 is a high-severity vulnerability in Weechat, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2021-09-05.
How severe is CVE-2021-40516?: High severity. CVSS v3 base score is 7.5 out of 10.