CVE-2021-40516: WeeChat before 3.2.1 allows remote attackers to cause a denial of service (crash) via a crafted WebSocket fram

This month

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATE

CVE-2021-40516 is a high-severity flaw (CVSS 7.5) affecting weechat, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-125
Published	2021-09-05
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · weechat

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-09-05 18:15 UTCPublished CVE record published
2026-06-17 04:07 UTCUpdated Record last modified

weechat weechat UPGRADE

Affected: >= 0.4.1 and < 3.2.1

Fixed in: 3.2.1

Safe to downgrade to: a release before 0.4.1

1. Check installed version

apt-cache policy weechat || rpm -q weechat || weechat --version

2. UPGRADE to 3.2.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade weechat

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade weechat

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.4.1 (Debian / Ubuntu)

apt-cache madison weechat sudo apt install weechat=<VERSION_BEFORE_0.4.1> sudo apt-mark hold weechat

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list weechat sudo dnf downgrade weechat-<VERSION_BEFORE_0.4.1> sudo dnf versionlock add weechat

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-40516?

weechat: upgrade to 3.2.1; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-40516 being exploited?

CVE-2021-40516 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-40516 affect?

CVE-2021-40516 affects weechat, debian linux. Severity is high (CVSS 7.5). 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.

How urgent is CVE-2021-40516?

Priority 55/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2024-46613 CRITICAL 9.8 UPGRADE WeeChat before 4.4.2 has an integer overflow and resultant buffer overflow at core/core-string.c when there ar
CVE-2022-28352 MEDIUM 4.3 UPGRADE WeeChat (aka Wee Enhanced Environment for Chat) 3.2 to 3.4 before 3.4.1 does not properly verify the TLS certi
CVE-2020-9760 CRITICAL 9.8 UPGRADE MITIGATE An issue was discovered in WeeChat before 2.7.1 (0.3.4 to 2.7 are affected)
CVE-2020-8955 CRITICAL 9.8 UPGRADE MITIGATE irc_mode_channel_update in plugins/irc/irc-mode.c in WeeChat through 2.7 allows remote attackers to cause a de

References

← Back to latest CVEs