chore(deps): update dependency postcss to v8.5.23 [security]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
postcss (source)	8.5.14 → 8.5.23

---

PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure

GHSA-r28c-9q8g-f849

More information

Details

Vulnerability Details

File: lib/previous-map.js
Line: 87-98 (loadFile), 129-144 (loadMap)

Root Cause

PostCSS auto-detects a /*# sourceMappingURL=... */ comment inside the CSS text it is asked to parse and, unless the caller explicitly passes map: false, attempts to load that path from disk as a "previous source map." This happens on every postcss.parse() / postcss().process() call by default (opt-out, not opt-in).

loadMap() builds the candidate path via join(dirname(opts.from), annotation), where annotation is the raw, attacker-controlled string from the CSS comment. path.join() normalizes but does not sandbox .. segments, so a ../../../ prefix walks the resolved path outside the intended directory. If opts.from is not set at all, the annotation is used completely unmodified — an absolute path in the CSS comment is read verbatim.

8.5.12 already fixed a strictly worse variant of this (any file, any extension, could be read) by requiring the resolved path to end in .map (loadFile()). That fix did not address the traversal itself, only the target extension. Since the join(dirname(file), map) logic has existed unchanged since PostCSS 8.0.0 (Feb 2020), any file ending in .map remains readable through this path in the current release (8.5.16).

Once loaded, MapGenerator.isMap() treats the mere presence of a loaded "previous map" as an implicit request to generate result.map, even when the caller never set the map option. If the loaded map has a sourcesContent field (common for maps emitted by bundlers/transpilers), that content is merged into result.map and returned to the caller — disclosing the traversed-to file's content to whoever supplied the CSS.

Attack Scenario

1. A service accepts user-submitted CSS and runs it through PostCSS to lint/format/transform it, e.g. postcss().process(userCss, { from: '/app/uploads/user123/input.css', to: '/app/uploads/user123/output.css' }) — idiomatic usage; map option untouched.
2. Attacker submits CSS containing /*# sourceMappingURL=../../../../some/other/app/dist/bundle.js.map */ (or an absolute path if from is unset).
3. PostCSS reads that .map file and folds its sourcesContent into result.map.
4. The service does what most build pipelines do with a truthy result.map — writes it next to the CSS output or returns it via API (source maps are meant to be consumed by browser devtools, so this is commonly public/served).
5. Attacker retrieves the emitted map and reads out the traversed file's content.

Impact

Disclosure of the contents of arbitrary .map files reachable via path traversal (or absolute path when from is unset) from the process's filesystem. Affects any application processing CSS it does not fully trust without explicitly passing map: false. No authentication or user interaction beyond submitting CSS text is required.

Vulnerable Code

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

loadMap(file, prev) {
  ...
  } else if (this.annotation) {
    let map = this.annotation
    if (file) map = join(dirname(file), map)
    let unknown = this.loadFile(map, file, false)
    ...
  }
}

Recommended Fix

Constrain the resolved path to remain inside the CSS file's own directory instead of relying solely on a filename-extension check:

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
    if (!cssFile) return undefined
    let root = resolve(dirname(cssFile))
    let resolvedPath = resolve(root, path)
    if (resolvedPath !== root && !resolvedPath.startsWith(root + sep)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

I've implemented, tested (full existing test suite — 660/660 passing, plus new PoC-based regression checks for both the traversal and legitimate same-directory cases), and can share this fix on request or via a private fork if invited.

Verification

Dynamically confirmed on v8.5.16 (current npm release / repo HEAD) via a standalone Node.js harness against lib/postcss.js: a "secret" .map file placed two directories outside a simulated project directory was read via a crafted sourceMappingURL comment in otherwise-innocuous CSS, with its sourcesContent appearing verbatim in result.map.toString() — with no map option set by the caller. A second harness confirmed the simpler no-from case reads an absolute path directly. A third harness confirmed map: false is the only current workaround. The attached fix branch closes both vectors while keeping all 660 existing unit tests green.

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References

• https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849
• https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c
• https://github.com/postcss/postcss/releases/tag/8.5.18
• https://github.com/advisories/GHSA-r28c-9q8g-f849

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

---

PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure

GHSA-r28c-9q8g-f849

More information

Details

Vulnerability Details

File: lib/previous-map.js
Line: 87-98 (loadFile), 129-144 (loadMap)

Root Cause

PostCSS auto-detects a /*# sourceMappingURL=... */ comment inside the CSS text it is asked to parse and, unless the caller explicitly passes map: false, attempts to load that path from disk as a "previous source map." This happens on every postcss.parse() / postcss().process() call by default (opt-out, not opt-in).

loadMap() builds the candidate path via join(dirname(opts.from), annotation), where annotation is the raw, attacker-controlled string from the CSS comment. path.join() normalizes but does not sandbox .. segments, so a ../../../ prefix walks the resolved path outside the intended directory. If opts.from is not set at all, the annotation is used completely unmodified — an absolute path in the CSS comment is read verbatim.

8.5.12 already fixed a strictly worse variant of this (any file, any extension, could be read) by requiring the resolved path to end in .map (loadFile()). That fix did not address the traversal itself, only the target extension. Since the join(dirname(file), map) logic has existed unchanged since PostCSS 8.0.0 (Feb 2020), any file ending in .map remains readable through this path in the current release (8.5.16).

Once loaded, MapGenerator.isMap() treats the mere presence of a loaded "previous map" as an implicit request to generate result.map, even when the caller never set the map option. If the loaded map has a sourcesContent field (common for maps emitted by bundlers/transpilers), that content is merged into result.map and returned to the caller — disclosing the traversed-to file's content to whoever supplied the CSS.

Attack Scenario

1. A service accepts user-submitted CSS and runs it through PostCSS to lint/format/transform it, e.g. postcss().process(userCss, { from: '/app/uploads/user123/input.css', to: '/app/uploads/user123/output.css' }) — idiomatic usage; map option untouched.
2. Attacker submits CSS containing /*# sourceMappingURL=../../../../some/other/app/dist/bundle.js.map */ (or an absolute path if from is unset).
3. PostCSS reads that .map file and folds its sourcesContent into result.map.
4. The service does what most build pipelines do with a truthy result.map — writes it next to the CSS output or returns it via API (source maps are meant to be consumed by browser devtools, so this is commonly public/served).
5. Attacker retrieves the emitted map and reads out the traversed file's content.

Impact

Disclosure of the contents of arbitrary .map files reachable via path traversal (or absolute path when from is unset) from the process's filesystem. Affects any application processing CSS it does not fully trust without explicitly passing map: false. No authentication or user interaction beyond submitting CSS text is required.

Vulnerable Code

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

loadMap(file, prev) {
  ...
  } else if (this.annotation) {
    let map = this.annotation
    if (file) map = join(dirname(file), map)
    let unknown = this.loadFile(map, file, false)
    ...
  }
}

Recommended Fix

Constrain the resolved path to remain inside the CSS file's own directory instead of relying solely on a filename-extension check:

loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
    if (!cssFile) return undefined
    let root = resolve(dirname(cssFile))
    let resolvedPath = resolve(root, path)
    if (resolvedPath !== root && !resolvedPath.startsWith(root + sep)) {
      return undefined
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()
  }
}

I've implemented, tested (full existing test suite — 660/660 passing, plus new PoC-based regression checks for both the traversal and legitimate same-directory cases), and can share this fix on request or via a private fork if invited.

Verification

Dynamically confirmed on v8.5.16 (current npm release / repo HEAD) via a standalone Node.js harness against lib/postcss.js: a "secret" .map file placed two directories outside a simulated project directory was read via a crafted sourceMappingURL comment in otherwise-innocuous CSS, with its sourcesContent appearing verbatim in result.map.toString() — with no map option set by the caller. A second harness confirmed the simpler no-from case reads an absolute path directly. A third harness confirmed map: false is the only current workaround. The attached fix branch closes both vectors while keeping all 660 existing unit tests green.

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References

• https://github.com/postcss/postcss/security/advisories/GHSA-r28c-9q8g-f849
• https://github.com/postcss/postcss/commit/95663d3eb7ba26f4854dd19d3b4f4425760cf56c
• https://github.com/postcss/postcss
• https://github.com/postcss/postcss/releases/tag/8.5.18

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

PostCSS: incomplete fix of GHSA-6g55-p6wh-862q — attacker-controlled sourceMappingURL reads arbitrary .map files when from is unset

CVE-2026-69153 / GHSA-fxqj-rqcc-2cmp

More information

Details

Summary

The fix for GHSA-6g55-p6wh-862q added a guard in lib/previous-map.js PreviousMap.loadFile() that restricts an attacker-controlled sourceMappingURL (from a CSS comment) to a .map extension and, for untrusted maps, rejects .. traversal and absolute paths. The traversal/absolute rejection is nested inside if (cssFile) { ... }. When PostCSS is invoked without the from option, cssFile is falsy and that branch is skipped, leaving only the .map extension check.

PreviousMap is constructed by lib/input.js whenever pathAvailable && sourceMapAvailable (under Node with source-map available), independent of opts.from/opts.map (the constructor returns early only for opts.map === false). So postcss([]).process(css) on attacker CSS reaches loadFile with cssFile undefined, and an attacker /*# sourceMappingURL=/abs/path/x.map */ (or ../-traversing path) is read via readFileSync. When the file is valid JSON, its sources (filesystem paths) and sourcesContent (source contents) are disclosed in the generated source map.

Affected code (v8.5.22 — the release carrying the GHSA-6g55 fix)

// lib/previous-map.js
loadFile(path, cssFile, trusted) {
  if (!trusted && !this.unsafeMap) {
    if (!/\.map$/i.test(path)) {
      return undefined
    }
    if (cssFile) {                       // guard runs ONLY when `from` is set
      let relativePath = relative(dirname(cssFile), path)
      if (relativePath === '..' ||
          relativePath.startsWith('..' + sep) ||
          isAbsolute(relativePath)) {
        return undefined
      }
    }
  }
  this.root = dirname(path)
  if (existsSync(path)) {
    this.mapFile = path
    return readFileSync(path, 'utf-8').toString().trim()   // sink
  }
}

// loadMap(): untrusted annotation path, trusted=false; file === opts.from
} else if (this.annotation) {
  let map = this.annotation
  if (file) map = join(dirname(file), map)   // no `from` -> map stays the raw URL
  let unknown = this.loadFile(map, file, false)  // file undefined -> cssFile falsy

Proof of concept (verified on postcss 8.5.22)

const postcss = require('postcss')
const fs = require('fs')

// a 'secret' sourcemap OUTSIDE any expected tree (stand-in for another project's .map)
const secret = '/tmp/pcpoc/secret_out_of_tree.map'
fs.writeFileSync(secret, JSON.stringify({
  version: 3, sources: ['/etc/REAL_PATH_LEAK'], mappings: '', names: [],
  sourcesContent: ['TOP_SECRET_abcdef']
}))

const css = 'a{color:red}\n/*# sourceMappingURL=' + secret + ' */'
const leaks = m => m && JSON.stringify(m.toJSON ? m.toJSON() : m).includes('TOP_SECRET_abcdef')

;(async () => {
  // A) NO `from`  -> guard skipped -> arbitrary absolute .map read + disclosed
  const a = await postcss([]).process(css, { map: true })
  console.log('no from   -> leaked:', !!leaks(a.map))   // true

  // B) WITH `from` -> guard active -> blocked
  const b = await postcss([]).process(css, { from: '/tmp/pcpoc/in.css', map: true })
  console.log('with from -> leaked:', !!leaks(b.map))    // false
})()

Observed output on postcss 8.5.22:

no from   -> leaked: true      # sourcesContent 'TOP_SECRET_abcdef' AND sources '/etc/REAL_PATH_LEAK' appear in result.map
with from -> leaked: false     # guard rejects the absolute path

../ traversal (no from) also succeeds; non-.map targets (.txt, ?x=.map, #.map) are blocked by the .map check. The tested build contains the GHSA-6g55 fix (this.json = JSON.parse(...) in loadMap, consumer() uses this.json || this.text), so this is a residual of that fix.

Impact

Arbitrary .map-file read (absolute path or ../ traversal) and disclosure of the target map's sources (local filesystem paths) and sourcesContent (source) into the generated source map, for any consumer that runs PostCSS on attacker-influenced CSS without a from option and exposes result.map (online CSS playgrounds, minify/lint services, string-input build steps). Bounded to files ending in .map that parse as JSON.

Suggested fix

Apply the traversal/absolute-path rejection to the untrusted map path regardless of whether cssFile is present (resolve against process.cwd() when there is no cssFile, and reject absolute paths and .. escape in all untrusted cases), or refuse to load an untrusted external map when no base file is known.

Severity

• CVSS Score: 6.3 / 10 (Medium)
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

References

• https://github.com/postcss/postcss/security/advisories/GHSA-fxqj-rqcc-2cmp
• https://github.com/postcss/postcss/commit/7beca139e70f9075c6b19700fcb00dd8033e5da8
• https://github.com/postcss/postcss
• https://github.com/postcss/postcss/releases/tag/8.5.19

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

---

Release Notes

postcss/postcss (postcss)

v8.5.23

Compare Source

• Do not load source map without opts.from for security reasons.

v8.5.22

Compare Source

• Fixed custom property losing semicolon before a comment (by @​sarathfrancis90).

v8.5.21

Compare Source

• Fixed childless at-rule losing semicolon before comment (by @​sarathfrancis90).
• Fixed docs (by @​isker).

v8.5.20

Compare Source

• Fixed missing space if AtRule#params is set after (by @​sarathfrancis90).
• Fixed mixing AST error on warnings (by @​MahinAnowar).

v8.5.19

Compare Source

• Fixed cleaning before for new nodes inserted to Root (by @​MahinAnowar).

v8.5.18

Compare Source

• Restricted loading previous source maps file to the opts.from folder for security reasons (use unsafeMap: true to disable the check).

v8.5.17

Compare Source

• Fixed Maximum call stack size exceeded error.
• Fixed Prototype hijacking for postcss.fromJSON().
• Fixed Input#origin() for unmapped end position (by @​chatman-media).

v8.5.16

Compare Source

• Fixed Input#origin() position (by @​mizdra).
• Fixed raws after rehydrating a JSON AST (by @​sarathfrancis90).
• Fixed putting parent-less node in nodes of new node (by @​MahinAnowar).
• Fixed computing offset in positionBy() (by @​greymoth-jp).
• Fixed rangeBy() on index: 0 (by @​sarathfrancis90).

v8.5.15

Compare Source

• Fixed declaration parsing performance (by @​homanp).

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