CVE-2026-45623
PostCSS: Arbitrary file read and information disclosure via attacker-controlled sourceMappingURL in CSS comments
Description
PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. In versions 8.5.11 and prior, the PreviousMap parses the /*# sourceMappingURL=PATH */ comment from any CSS string passed to process() and dereferences PATH against the local filesystem with no scheme, allowlist, or traversal check. An attacker who controls the CSS input can cause the host process to read any file readable by Node and leak the first ~10 bytes of its content through the resulting JSON.parse SyntaxError message. The bug also yields a precise file-existence oracle and a controllable-read primitive that may be combined with large-file targets for DoS. The behaviour is triggered with PostCSS's default options — no from, no map, no plugins required — and is therefore reachable from any pipeline that runs untrusted CSS through PostCSS (CMS themes, user-uploaded styles, browser-extension/userstyle processors, build pipelines for third-party packages, blog comment renderers, etc.). This issue has been fixed in version 8.5.12.
INFO
Published Date :
July 27, 2026, 6:16 p.m.
Last Modified :
Aug. 7, 2026, 12:13 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE | ||||
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update PostCSS to version 8.5.12 or later.
- Review CSS input sources for untrusted content.
- Consider input sanitization for CSS.
- Apply security patches promptly.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-45623.
| URL | Resource |
|---|---|
| https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q | Exploit Mitigation Vendor Advisory |
| https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q | Exploit Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-45623 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-45623
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-45623 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-45623 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Aug. 07, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:postcss:postcss:*:*:*:*:*:node.js:*:* versions up to (excluding) 8.5.12 Added Reference Type GitHub, Inc.: https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q Types: Exploit, Mitigation, Vendor Advisory Added Reference Type CISA-ADP: https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q Types: Exploit, Mitigation, Vendor Advisory -
New CVE Received by [email protected]
Jul. 27, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'postcss', 'product': 'postcss', 'versions': [{'status': 'affected', 'version': '< 8.5.12'}]}] Added Description PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. In versions 8.5.11 and prior, the PreviousMap parses the /*# sourceMappingURL=PATH */ comment from any CSS string passed to process() and dereferences PATH against the local filesystem with no scheme, allowlist, or traversal check. An attacker who controls the CSS input can cause the host process to read any file readable by Node and leak the first ~10 bytes of its content through the resulting JSON.parse SyntaxError message. The bug also yields a precise file-existence oracle and a controllable-read primitive that may be combined with large-file targets for DoS. The behaviour is triggered with PostCSS's default options — no from, no map, no plugins required — and is therefore reachable from any pipeline that runs untrusted CSS through PostCSS (CMS themes, user-uploaded styles, browser-extension/userstyle processors, build pipelines for third-party packages, blog comment renderers, etc.). This issue has been fixed in version 8.5.12. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Added CWE CWE-22 Added CWE CWE-200 Added Reference https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 27, 2026
Action Type Old Value New Value Added Reference https://github.com/postcss/postcss/security/advisories/GHSA-6g55-p6wh-862q Added SSVC {'id': 'CVE-2026-45623', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-27T17:44:10.727948Z'}