CVE-2020-24916: CGI implementation in Yaws web server versions 1.81 to 2.0.7 is vulnerable to OS command injection.

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CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2020-24916 is a critical-severity flaw (CVSS 9.8) affecting yaws, ubuntu linux, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

CGI implementation in Yaws web server versions 1.81 to 2.0.7 is vulnerable to OS command injection.

Why this priority

Critical severity
EPSS top 3%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	17.4% (top 3%)
CISA exploited list	No
Weakness	CWE-78
Published	2020-09-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: canonical · debian · yaws

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

Am I affected?

Timeline

2020-09-09 19:15 UTCPublished CVE record published
2026-06-17 03:06 UTCUpdated Record last modified

yaws yaws UPGRADE

Affected: >= 1.81 and <= 2.0.7

Fixed in: newer than 2.0.7

Safe to downgrade to: a release before 1.81

1. Check installed version

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

2. UPGRADE to newer than 2.0.7 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade yaws

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 1.81 (Debian / Ubuntu)

apt-cache madison yaws sudo apt install yaws=<VERSION_BEFORE_1.81> sudo apt-mark hold yaws

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

dnf --showduplicates list yaws sudo dnf downgrade yaws-<VERSION_BEFORE_1.81> sudo dnf versionlock add yaws

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.

canonical ubuntu linux MITIGATE

Affected: 18.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 18.04

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 · 10.0

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · shotcut · FIXED · 26.10.30-1.fc46 · FEDORA-2026-7787c7fc2d · source

sudo dnf upgrade --advisory=FEDORA-2026-7787c7fc2d

Ubuntu 20.04 · yaws · NO FIX YET

Ubuntu 22.04 · yaws · NOT AFFECTED

Ubuntu 24.04 · yaws · NOT AFFECTED

Ubuntu 24.10 · yaws · NOT AFFECTED

Ubuntu 25.04 · yaws · NOT AFFECTED

Debian 12 · yaws · FIXED · 2.0.8+dfsg-1

sudo apt update && sudo apt install --only-upgrade yaws dpkg --compare-versions "$(dpkg-query -W -f='${Version}' yaws)" ge "2.0.8+dfsg-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · yaws · FIXED · 2.0.8+dfsg-1

sudo apt update && sudo apt install --only-upgrade yaws dpkg --compare-versions "$(dpkg-query -W -f='${Version}' yaws)" ge "2.0.8+dfsg-1" && echo PATCHED || echo STILL-VULNERABLE

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/vulnbe/poc-yaws-cgi-shell-injection
Write-up: packetstormsecurity.com/files/159106/Yaws-2.0.7-XML-Injection-Command-Injection.html
Write-up: vuln.be/post/yaws-xxe-and-shell-injections/
GitHub PoC: Live-Hack-CVE/CVE-2020-24916

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-2020-24916?

yaws: upgrade to newer than 2.0.7; ubuntu linux: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-24916 being exploited?

CVE-2020-24916 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-2020-24916 affect?

CVE-2020-24916 affects yaws, ubuntu linux, debian linux. Severity is critical (CVSS 9.8). CGI implementation in Yaws web server versions 1.81 to 2.0.7 is vulnerable to OS command injection.

How urgent is CVE-2020-24916?

Priority 74/100. Critical severity; EPSS top 3%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Ubuntu vulnerabilities · Debian vulnerabilities

Related CVEs

CVE-2020-24379 CRITICAL 9.8 UPGRADE MITIGATE WebDAV implementation in Yaws web server versions 1.81 to 2.0.7 is vulnerable to XXE injection.
CVE-2020-12872 MEDIUM 5.5 UPGRADE yaws_config.erl in Yaws through 2.0.2 and/or 2.0.7 loads obsolete TLS ciphers, as demonstrated by ones that al
CVE-2017-10974 HIGH 7.5 DOWNGRADE Yaws 1.91 allows Unauthenticated Remote File Disclosure via HTTP Directory Traversal with /%5C../ to port 8080
CVE-2016-1000108 MEDIUM 6.1 UPGRADE MITIGATE yaws before 2.0.4 does not attempt to address RFC 3875 section 4.1.18 namespace conflicts and therefore does n
CVE-2011-4350 MEDIUM 6.5 DOWNGRADE MITIGATE Yaws 1.91 has a directory traversal vulnerability in the way certain URLs are processed

References

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