Node postcss: PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. (CVE-2026-45623)
A vulnerability in node-postcss versions 8.5.11 and earlier allows an attacker controlling CSS input to cause the host process to read arbitrary local files. This occurs because the PreviousMap feature dereferences sourceMappingURL comments against the local filesystem without proper validation. The flaw can leak file content bytes via JSON.parse error messages and can be used as a file-existence oracle or to cause denial of service. The issue is fixed in version 8.5.12.
AI Analysis
Technical Summary
Node-postcss versions 8.5.11 and prior contain a vulnerability in the PreviousMap feature where the sourceMappingURL comment in CSS is parsed and dereferenced against the local filesystem without scheme, allowlist, or traversal checks. An attacker who controls the CSS input can exploit this to read the first ~10 bytes of any file readable by Node.js, leak file existence information, and potentially cause denial of service with large file reads. This behavior is triggered with default PostCSS options and requires no plugins or additional configuration. The vulnerability is fixed in version 8.5.12.
Potential Impact
An attacker able to supply CSS input to a PostCSS processing pipeline can read arbitrary local files partially, leak file existence information, and potentially cause denial of service by reading large files. This can lead to information disclosure and service disruption. The vulnerability does not require privileges or user interaction and is remotely exploitable if untrusted CSS is processed.
Mitigation Recommendations
Upgrade node-postcss to version 8.5.12 or later, where this vulnerability is fixed. Avoid processing untrusted CSS with vulnerable versions. Patch status is confirmed fixed in 8.5.12. No other mitigations are indicated.
Node postcss: PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. (CVE-2026-45623)
Description
A vulnerability in node-postcss versions 8.5.11 and earlier allows an attacker controlling CSS input to cause the host process to read arbitrary local files. This occurs because the PreviousMap feature dereferences sourceMappingURL comments against the local filesystem without proper validation. The flaw can leak file content bytes via JSON.parse error messages and can be used as a file-existence oracle or to cause denial of service. The issue is fixed in version 8.5.12.
CVSS v3.1
Score 9.1critical
Affected software
pkg:deb/ubuntu/node-postcss?arch=source&distro=focalpkg:deb/ubuntu/node-postcss?arch=source&distro=jammypkg:deb/ubuntu/node-postcss?arch=source&distro=noblepkg:deb/ubuntu/node-postcss?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Node-postcss versions 8.5.11 and prior contain a vulnerability in the PreviousMap feature where the sourceMappingURL comment in CSS is parsed and dereferenced against the local filesystem without scheme, allowlist, or traversal checks. An attacker who controls the CSS input can exploit this to read the first ~10 bytes of any file readable by Node.js, leak file existence information, and potentially cause denial of service with large file reads. This behavior is triggered with default PostCSS options and requires no plugins or additional configuration. The vulnerability is fixed in version 8.5.12.
Potential Impact
An attacker able to supply CSS input to a PostCSS processing pipeline can read arbitrary local files partially, leak file existence information, and potentially cause denial of service by reading large files. This can lead to information disclosure and service disruption. The vulnerability does not require privileges or user interaction and is remotely exploitable if untrusted CSS is processed.
Mitigation Recommendations
Upgrade node-postcss to version 8.5.12 or later, where this vulnerability is fixed. Avoid processing untrusted CSS with vulnerable versions. Patch status is confirmed fixed in 8.5.12. No other mitigations are indicated.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-45623
- Osv Schema Version
- 1.7.0
- Aliases
- []
- Ecosystems
- ["Ubuntu:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.04:LTS"]
- Database Specific Severity
- null
- Cvss Version
- 3.1
Threat ID: 6a774343bf8831d539b47b87
Added to database: 08/08/2026, 14:54:59 UTC
Last enriched: 08/08/2026, 15:44:25 UTC
Last updated: 08/08/2026, 16:12:34 UTC
Views: 5
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