CVE-2021-33477: rxvt-unicode 9.22, rxvt 2.7.10, mrxvt 0.5.4, and Eterm 0.9.7 allow (potentially remote) code execution because

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HIGH 8.8WATCHLISTDOWNGRADEDOWNGRADEDOWNGRADE

CVE-2021-33477 is a high-severity flaw (CVSS 8.8) affecting eterm, mrxvt, rxvt-unicode. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

rxvt-unicode 9.22, rxvt 2.7.10, mrxvt 0.5.4, and Eterm 0.9.7 allow (potentially remote) code execution because of improper handling of certain escape sequences (ESC G Q). A response is terminated by a newline.

Why this priority

High severity
EPSS top 9%: very likely to be exploited
Public exploit reference
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	4.1% (top 9%)
CISA exploited list	No
Weakness	CWE-755
Published	2021-05-20
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · eterm project · fedoraproject · mrxvt project · rxvt project · rxvt-unicode project

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

Am I affected?

Timeline

2021-05-20 20:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

eterm project eterm DOWNGRADE

Affected: 0.9.7

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.9.7

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.9.7 (Debian / Ubuntu)

apt-cache madison eterm sudo apt install eterm=<VERSION_BEFORE_0.9.7> sudo apt-mark hold eterm

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list eterm sudo dnf downgrade eterm-<VERSION_BEFORE_0.9.7> sudo dnf versionlock add eterm

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.

mrxvt project mrxvt DOWNGRADE

Affected: 0.5.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.5.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.5.4 (Debian / Ubuntu)

apt-cache madison mrxvt sudo apt install mrxvt=<VERSION_BEFORE_0.5.4> sudo apt-mark hold mrxvt

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mrxvt sudo dnf downgrade mrxvt-<VERSION_BEFORE_0.5.4> sudo dnf versionlock add mrxvt

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.

rxvt-unicode project rxvt-unicode DOWNGRADE

Affected: 9.22

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.22

1. Check installed version

apt-cache policy rxvt-unicode || rpm -q rxvt-unicode || rxvt-unicode --version

2. No fixed release: DOWNGRADE to a release before 9.22 (Debian / Ubuntu)

apt-cache madison rxvt-unicode sudo apt install rxvt-unicode=<VERSION_BEFORE_9.22> sudo apt-mark hold rxvt-unicode

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list rxvt-unicode sudo dnf downgrade rxvt-unicode-<VERSION_BEFORE_9.22> sudo dnf versionlock add rxvt-unicode

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.

rxvt project rxvt DOWNGRADE

Affected: 2.7.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.7.10

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2.7.10 (Debian / Ubuntu)

apt-cache madison rxvt sudo apt install rxvt=<VERSION_BEFORE_2.7.10> sudo apt-mark hold rxvt

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list rxvt sudo dnf downgrade rxvt-<VERSION_BEFORE_2.7.10> sudo dnf versionlock add rxvt

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.

fedoraproject fedora MITIGATE

Affected: 33 · 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

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.

debian debian linux MITIGATE

Affected: 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

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-2021-33477?

eterm: downgrade or apply the listed mitigation; mrxvt: downgrade or apply the listed mitigation; rxvt-unicode: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-33477 being exploited?

CVE-2021-33477 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-2021-33477 affect?

CVE-2021-33477 affects eterm, mrxvt, rxvt-unicode. Severity is high (CVSS 8.8). rxvt-unicode 9.22, rxvt 2.7.10, mrxvt 0.5.4, and Eterm 0.9.7 allow (potentially remote) code execution because of improper handling of certain escape sequences (ESC G Q). A response is terminated by a newline.

How urgent is CVE-2021-33477?

Priority 63/100. High severity; EPSS top 9%: very likely to be exploited; Public exploit reference; On your watchlist

Software pages

Debian vulnerabilities

References

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