CVE-2019-3902: Mercurial Path Traversal Vulnerability

MODERATE
Advisory Identifier: GHSA-mq66-vcfc-8246
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CVSS 5.9
CWE-59 CWE-22
Published
Advisory Summary

CVE-2019-3902 is a MODERATE (CVSS 5.9) path traversal vulnerability (CWE-59: Improper Link Resolution Before File Access ('Link Following')) affecting Mercurial libraries in the PyPI ecosystem. The issue involves mercurial path traversal/link following vulnerability. Remediation is available by upgrading affected packages to version 4.9.

CVE-2019-3902 at a Glance

CVE Identifier CVE-2019-3902
GHSA Identifier GHSA-mq66-vcfc-8246
Severity MODERATE
CVSS v3.1 Base Score 5.9
CWE Classification CWE-59: Improper Link Resolution Before File Access ('Link Following')
Affected Product Mercurial
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.9

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2019-3902

To remediate this vulnerability, upgrade all affected Mercurial dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mercurial fixed: 4.9 
pip install mercurial>=4.9
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show mercurial

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2019-3902, inspect your installed packages using pip:

pip show mercurial

Analyze the terminal output to locate any version of Mercurial in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.9), your application is affected.

Note: The pip show mercurial command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-59: Improper Link Resolution Before File Access ('Link Following'), where the product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource. In Mercurial, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2019-3902 Affected Mercurial Versions

1 component(s)
Fixed Versions:
4.9
Product / Package Ecosystem Affected Versions Fixed Version
mercurial
pypi/mercurial
PyPI
< 4.9
4.9

References

NVD — CVE-2019-3902 NVD
https://nvd.nist.gov/vuln/detail/CVE-2019-3902
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3902
Mercurial Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/mercurial/PYSEC-2019-188.yaml
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2019/04/msg00024.html
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2020/07/msg00032.html
usn.ubuntu.com/4086-1 WEB
https://usn.ubuntu.com/4086-1
Mercurial Security Information SECURITY
https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.9_.282019-02-01.29

Frequently Asked Questions

What is CVE-2019-3902?
CVE-2019-3902 is a security vulnerability in Mercurial involving Mercurial Path Traversal/Link Following vulnerability under CWE-59: Improper Link Resolution Before File Access ('Link Following').
Which Mercurial versions are affected?
Affected versions include releases prior to 4.9 across affected packages: mercurial.
What version fixes CVE-2019-3902?
Upgrading to 4.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mercurial affected?
Yes, mercurial is affected in releases prior to 4.9. Upgrade your dependency to 4.9 or later.
What is the CVSS score of CVE-2019-3902?
CVE-2019-3902 has a CVSS v3.1 base score of 5.9 (MODERATE) with vector string CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2019-3902?
CVE-2019-3902 is classified under CWE-59: Improper Link Resolution Before File Access ('Link Following') (The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.).
How can I check PyPI dependencies for CVE-2019-3902?
Run the dependency tree command: 'pip show mercurial'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mq66-vcfc-8246",
  "modified" : "2024-09-25T19:41:29Z",
  "published" : "2022-02-15T01:13:11Z",
  "aliases" : [ "CVE-2019-3902" ],
  "summary" : "Mercurial Path Traversal/Link Following vulnerability",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mercurial"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2019-3902"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3902"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/mercurial/PYSEC-2019-188.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2019/04/msg00024.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2020/07/msg00032.html"
  }, {
    "type" : "WEB",
    "url" : "https://usn.ubuntu.com/4086-1"
  }, {
    "type" : "WEB",
    "url" : "https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.9_.282019-02-01.29"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-59" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2024-05-01T16:49:25Z",
    "nvd_published_at" : "2019-04-22T16:29:00Z"
  }
}