CVE-2026-83606 xmldom PI grammar regex ReDoS: quadratic backtracking on unterminated processing instructions
An attacker can cause a denial of service by sending a small, malformed XML input that triggers quadratic backtracking in the parser, stalling the application.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-83606?
CVE-2026-83606 is a high-severity denial of service vulnerability in @xmldom xmldom, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-83606?
2 open source packages ship an affected version, including @xmldom/xmldom.
| Package | Affected | Fixed in |
|---|---|---|
@xmldom/xmldom npm | From 0.9.0-beta.9 | 0.9.11 |
@xmldom/xmldom npm | From 0.9.0-beta.9 | 0.9.11 |
How do I fix CVE-2026-83606?
Upgrade @xmldom/xmldom to 0.9.11 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-83606 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-83606 exists.
Sources
Also known as CLSA-2026-1791369737, DEBIAN-CVE-2026-83606, GHSA-g53g-w8rj-fmg7, UBUNTU-CVE-2026-83606.