Skip to content
Patch Next
Sign inAdd to your agent

← Actionable
High, CVSS 8.7amended

xmldom PI grammar regex ReDoS: quadratic backtracking on unterminated processing instructions

CVE-2026-83606GHSA-g53g-w8rj-fmg7

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@xmldom/xmldom 0.9.11), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

Add to your agent

Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-83606: 0.52% estimated exploitation activity in the next 30 days; percentile 44.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary @xmldom/xmldom's processing-instruction (PI) grammar regex exhibits quadratic-time backtracking (ReDoS) when parsing an unterminated processing instruction. A single small XML document containing <? + a target + a long run of whitespace and no closing ? forces the regular expression engine into O(n²) work, stalling the Node.js event loop. The input is parsed with DOMParser.parseFromString under default options, so it is reachable from unauthenticated, network-delivered XML (SOAP/SAML, webhooks, uploads, XML APIs). Details The PI production in lib/grammar.js compiles (flags mu) to: - lib/grammar.js line 261: https://github.com/xmldom/xmldom/blob/bb7a085dc5ba1eea3212388509b97bb4b4af32b9/lib/grammar.js#L261 In the optional tail (?:S+(Char?))?, both the greedy separator S+ and the lazy data Char? match XML whitespace. When the required trailing ? is absent, the engine must ultimately fail — but first it tries every partition of the whitespace run between S+ and Char?, which is…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-g53g-w8rj-fmg7

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-g53g-w8rj-fmg7

  4. Revision 1 · created ·

    Published from ghsa record GHSA-g53g-w8rj-fmg7

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-83606

Advisory: xmldom PI grammar regex ReDoS: quadratic backtracking on unterminated processing instructions
IDs: CVE-2026-83606, GHSA-g53g-w8rj-fmg7
Record: https://patchnext.com/advisories/cve-2026-83606 (revision 4, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @xmldom/xmldom 0.9.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @xmldom/xmldom: affected >= 0.9.0-beta.9, <= 0.9.10; fixed in 0.9.11

## Suggested inspection (read-only)
- `npm ls @xmldom/xmldom --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @xmldom/xmldom.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g53g-w8rj-fmg7 (GitHub-reviewed advisory GHSA-g53g-w8rj-fmg7 lists affected ranges: npm @xmldom/xmldom >=0.9.0-beta.9 <=0.9.10)
- Verified: https://osv.dev/vulnerability/GHSA-g53g-w8rj-fmg7 (OSV record GHSA-g53g-w8rj-fmg7 lists affected ranges: npm @xmldom/xmldom >=0.9.0-beta.9 <0.9.11 (fixed))

Commands are suggestions: review each one before running it.

Loading voting…