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CVE-2026-45623— PostCSS: Arbitrary file read and information disclosure via attacker-controlled sourceMappingURL in CSS comments

Quick assessment

Affected
postcss postcss
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

PostCSS 接收一个 CSS 文件，并通过将规则转换为抽象语法树（Abstract Syntax Tree, AST），提供分析和修改这些规则的 API。在版本 8.5.11 及更早版本中，PreviousMap 会解析通过 函数传入的任意 CSS 字符串中的 注释，并针对本地文件系统对 PATH 进行解引用，过程中未使用任何协议前缀（scheme）、白名单或路径遍历检查。攻击者若能控制 CSS 输入，便可促使主机进程读取 Node.js 环境下可读的任何文件，并通过由此触发的 语法错误消息，泄露该文件内容的前

CVSS 7.5 · High EPSS 0.61% · P47

Affected Version Matrix 1

VendorProduct Version RangeStatus
postcss postcss < 8.5.12 affected
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I. Basic Information for CVE-2026-45623

Vulnerability Information
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Vulnerability Title
PostCSS: Arbitrary file read and information disclosure via attacker-controlled sourceMappingURL in CSS comments
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
postcss postcss < 8.5.12 -

II. Public POCs for CVE-2026-45623

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8875 chars
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III. Intelligence Information for CVE-2026-45623

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Vendor Advisories for CVE-2026-45623 (1)

IV. Related Vulnerabilities

Same product: postcss
Same vendor: postcss
Same weakness: CWE-22

V. Comments for CVE-2026-45623

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