CVE-2020-27347: In tmux before version 3.1c the function input_csi_dispatch_sgr_colon() in file input.c contained a stack-base

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HIGH 8.8UPGRADE

CVE-2020-27347 is a high-severity flaw (CVSS 8.8) affecting tmux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In tmux before version 3.1c the function input_csi_dispatch_sgr_colon() in file input.c contained a stack-based buffer-overflow that can be exploited by terminal output.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.7% (top 47%)
CISA exploited list	No
Weakness	CWE-121, CWE-787
Published	2020-11-06
Last modified	2026-06-17

Publisher (CNA): Canonical Ltd. · Vendor: tmux project

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

Am I affected?

Timeline

2020-11-06 03:15 UTCPublished CVE record published
2026-06-17 03:09 UTCUpdated Record last modified

tmux project tmux UPGRADE

Affected: >= 2.9 and <= 3.1b

Fixed in: newer than 3.1b

Safe to downgrade to: a release before 2.9

1. Check installed version

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

2. UPGRADE to newer than 3.1b (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade tmux

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 2.9 (Debian / Ubuntu)

apt-cache madison tmux sudo apt install tmux=<VERSION_BEFORE_2.9> sudo apt-mark hold tmux

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

dnf --showduplicates list tmux sudo dnf downgrade tmux-<VERSION_BEFORE_2.9> sudo dnf versionlock add tmux

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.

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-2020-27347?

tmux: upgrade to newer than 3.1b. Exact commands for each OS are on this page.

Is CVE-2020-27347 being exploited?

CVE-2020-27347 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-2020-27347 affect?

CVE-2020-27347 affects tmux. Severity is high (CVSS 8.8). In tmux before version 3.1c the function input_csi_dispatch_sgr_colon() in file input.c contained a stack-based buffer-overflow that can be exploited by terminal output.

How urgent is CVE-2020-27347?

Priority 49/100. High severity; Public exploit reference

References

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