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CRITICAL severity

CVE-2018-17983 — mercurial

CRITICAL

CVE-2018-17983 is a critical-severity (CVSS 9.1) Out-of-bounds Read vulnerability in mercurial. A fix is available for mercurial — see the affected versions and patch details below.

Mercurial Out-of-bounds Read vulnerability

Also known asGHSA-p575-cf9h-wv42PYSEC-2018-91
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.0%probability of exploitation in next 30 days
Lower Risk-0.08%
Lower risk than most CVEs80th percentile — riskier than 80% of all scored CVEsHighest risk
0.00%0.85%1.70%2.55%0.4%2.0%May 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍mercurial

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

cext/manifest.c in Mercurial before 4.7.2 has an out-of-bounds read during parsing of a malformed manifest entry.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPImercurialall versions4.7.2pip install --upgrade 'mercurial==4.7.2'

Affected Products

1 product · 1 configurations
Application
mercurialmercurial
< 4.7.2
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mercurial, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update mercurial to 4.7.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-17983 is resolved across your whole dependency graph.

  3. Workarounds

    Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

UbuntuCRITICAL
USN-5102-1UbuntuUSN-5102-2Ubuntu

Frequently Asked Questions

cext/manifest.c in Mercurial before 4.7.2 has an out-of-bounds read during parsing of a malformed manifest entry.
O3 Security · Impact-Aware SCA

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CVE-2018-17983: mercurial — Fixed in 4.7.2