Summary
xmldom: End-tag Whitespace-Trim Regex ReDoS, quadratic backtracking in the 0.8.x end-tag parser
On the @xmldom/xmldom 0.8.x line, parsing an XML end tag whose name is followed by a long run
of whitespace and then a non-whitespace character triggers quadratic-time regular-expression
backtracking (ReDoS), so a single small crafted end tag stalls the Node.js event loop. It is reachable
from DOMParser.parseFromString under default options, unauthenticated, before any validity
check, an availability-only denial of service. The 0.9.x line is not affected.
Details
lib/sax.js (release-0.8.x, commit e5c1480) trims trailing whitespace from a captured end-tag name
with an unanchored global regex:
lib/sax.jsline 120: https://github.com/xmldom/xmldom/blob/e5c14802592685bb872c042c54c3f73758875c85/lib/sax.js#L120
/[ \t\n\r]+$/g
Applied to a string shaped whitespace-run + one non-whitespace char (e.g. the content of an end tag</ … x>), the engine must, for every starting position, extend [ws]+ to the end and then fail
the $ anchor when the trailing non-whitespace char is present, classic O(n²) backtracking in the
length of the whitespace run. The trimmed substring is delimited only by indexOf('>'), so the
attacker controls its length directly.
Proof of Concept
const { DOMParser } = require('@xmldom/xmldom'); // 0.8.x
const n = 64 * 1024;
const payload = '<r></' + ' '.repeat(n) + 'x>';
console.time('parse');
new DOMParser().parseFromString(payload, 'text/xml');
console.timeEnd('parse');
Measured (Node 18), time quadruples per doubling of the whitespace run (canonical O(n²)):
| Whitespace run | Isolated regex | End-to-end parseFromString (0.8.13) |
|---|---|---|
| 4 KB | 5.6 ms | 5.7 ms |
| 8 KB | 22.7 ms | 22.5 ms |
| 16 KB | 88.6 ms | 92 ms |
| 32 KB | 354 ms | 361 ms |
| 64 KB | 1434 ms | 1452 ms |
| 128 KB | 5761 ms | , |
Affected Versions
Affected on the 0.7.x and 0.8.x lines (the trailing-whitespace trim was added in 0.7.0, present
through 0.8.14); the fix targets the 0.8.x LTS patch. The 0.9.x line rewrote end-tag parsing to
an anchored linear matcher and never had this regex, so it is not affected. No published unscopedxmldom is affected, the vulnerable code exists only in a 0.7.0 git tag that was never released to
npm (npm view xmldom → latest = 0.6.0).
Fix Applied
Anchors the end-tag trailing-whitespace trim so it runs in linear time instead of
backtracking quadratically on a long whitespace run. Byte-identical output. Non-breaking; 0.8.x-only.
Severity note
The complexity is quadratic, not exponential, so a multi-second stall requires
tens-to-hundreds of KB of input. VA:H reflects that xmldom applies no input-size limit and the
path runs on default-options parsing, so a single unbounded parse can fully stall the event loop.
Impact
Availability only: a single parse of a small crafted document blocks the Node.js event loop for the
duration of the quadratic scan (≈1.4 s at 64 KB; multi-second with larger inputs). No memory
blow-up, no data exposure, no integrity impact. Because XML is routinely accepted from untrusted
sources and parsed with default options, one request can stall a server.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-83619? CVE-2026-83619 is a high-severity uncontrolled resource consumption vulnerability in @xmldom/xmldom (npm), affecting versions >= 0.7.0, <= 0.8.14. It is fixed in 0.8.15. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- Which versions of @xmldom/xmldom are affected by CVE-2026-83619? @xmldom/xmldom (npm) versions >= 0.7.0, <= 0.8.14 is affected.
- Is there a fix for CVE-2026-83619? Yes. CVE-2026-83619 is fixed in 0.8.15. Upgrade to this version or later.
- Is CVE-2026-83619 exploitable, and should I be worried? Whether CVE-2026-83619 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-83619 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-83619? Upgrade
@xmldom/xmldomto 0.8.15 or later.