CVE-2017-12836: CVS 1.12.x, when configured to use SSH for remote repositories, might allow remote attackers to execute arbitr

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HIGH 7.5WATCHLISTDOWNGRADEMITIGATEMITIGATE

CVE-2017-12836 is a high-severity flaw (CVSS 7.5) affecting cvs, ubuntu linux, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

CVS 1.12.x, when configured to use SSH for remote repositories, might allow remote attackers to execute arbitrary code via a repository URL with a crafted hostname, as demonstrated by "-oProxyCommand=id;localhost:/bar."

Why this priority

High severity
EPSS top 6%: 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	7.5 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	6.6% (top 6%)
CISA exploited list	No
Published	2017-08-24
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2017-08-24 14:29 UTCPublished CVE record published
2026-06-17 01:04 UTCUpdated Record last modified

gnu cvs DOWNGRADE

Affected: 1.12.1 · 1.12.3 · 1.12.5 · 1.12.6 · 1.12.7 · 1.12.9 · 1.12.10 · 1.12.11

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.12.1

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.12.1 (Debian / Ubuntu)

apt-cache madison cvs sudo apt install cvs=<VERSION_BEFORE_1.12.1> sudo apt-mark hold cvs

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

dnf --showduplicates list cvs sudo dnf downgrade cvs-<VERSION_BEFORE_1.12.1> sudo dnf versionlock add cvs

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: 14.04 · 16.04 · 17.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 14.04

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: 8.0 · 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

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-2017-12836?

cvs: downgrade or apply the listed mitigation; 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-2017-12836 being exploited?

CVE-2017-12836 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-2017-12836 affect?

CVE-2017-12836 affects cvs, ubuntu linux, debian linux. Severity is high (CVSS 7.5). CVS 1.12.x, when configured to use SSH for remote repositories, might allow remote attackers to execute arbitrary code via a repository URL with a crafted hostname, as demonstrated by "-oProxyCommand=id;localhost:/bar."

How urgent is CVE-2017-12836?

Priority 60/100. High severity; EPSS top 6%: very likely to be exploited; Public exploit reference; On your watchlist

Software pages

Ubuntu vulnerabilities · Debian vulnerabilities

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References

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