UBUNTU-CVE-2026-121438

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Source
https://ubuntu.com/security/CVE-2026-121438
Import Source
https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json
JSON Data
https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-121438
Upstream
Published
2026-11-03T15:17:00Z
Modified
2026-11-05T11:46:31Z
Severity
  • 5.3 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L CVSS Calculator
  • 6.9 (Medium) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N CVSS Calculator
  • Ubuntu - medium
Summary
[none]
Details

Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.

References

Affected packages

Ubuntu:16.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=xenial

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

0.*
0.6-2
0.7.1-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python-mistune",
            "binary_version": "0.7.1-1"
        },
        {
            "binary_name": "python3-mistune",
            "binary_version": "0.7.1-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:18.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=bionic

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

0.*
0.7.4-1
0.8-1
0.8.1-1
0.8.3-2

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python-mistune",
            "binary_version": "0.8.3-2"
        },
        {
            "binary_name": "python3-mistune",
            "binary_version": "0.8.3-2"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:20.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=focal

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

0.*
0.8.4-1
0.8.4-2

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python3-mistune",
            "binary_version": "0.8.4-2"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:22.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=jammy

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

0.*
0.8.4-4
0.8.4-5
2.*
2.0.0-1+really0.8.4-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python3-mistune",
            "binary_version": "2.0.0-1+really0.8.4-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:24.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=noble

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

2.*
2.0.4-2
3.*
3.0.2-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python3-mistune",
            "binary_version": "3.0.2-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:26.04:LTS
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=resolute

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

3.*
3.1.3-1
3.1.4-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python3-mistune",
            "binary_version": "3.1.4-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"
Ubuntu:26.10
mistune

Package

Name
mistune
Purl
pkg:deb/ubuntu/mistune?arch=source&distro=stonking

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

3.*
3.1.4-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "python3-mistune",
            "binary_version": "3.1.4-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-121438.json"