CVE-2026-73643 js-yaml: Exponential parsing time in the flow collections leads to denial of service
Attackers can cause denial of service by submitting small YAML inputs that trigger exponential parsing time, blocking the Node.js event loop.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-73643?
CVE-2026-73643 is a high-severity denial of service vulnerability in nodeca js-yaml, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 until 5.2.2, parsing a small YAML document can take exponential time when an application calls load() or loadAll() on untrusted input. In src/parser/parser.ts, readFlowCollection uses restoreState and calls parseNode a second time when a flow-sequence entry is recognized as a key: value pair. If the key is a nested flow sequence of the same shape, every level is parsed twice, causing O(2^n) work and allowing an input under 200 bytes to keep one CPU busy for minutes, block the Node.js event loop, and stall the process. No anchors, aliases, merges, tags, or nondefault options are required. This issue is fixed in version 5.2.2.
Weakness: CWE-407
Which versions are affected by CVE-2026-73643?
2 open source packages ship an affected version, including js-yaml.
| Package | Affected | Fixed in |
|---|---|---|
js-yaml npm | From 5.0.0 | 5.2.2 |
js-yaml npm | From 5.0.0 | 5.2.2 |
How do I fix CVE-2026-73643?
Upgrade js-yaml to 5.2.2 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-2026-73643 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73643 exists.
Sources
Also known as CLSA-2026-1792473248, GHSA-pm4m-ph32-ghv5, ROOT-APP-NPM-CVE-2026-73643, ROOT-APP-NPM-GHSA-pm4m-ph32-ghv5, UBUNTU-CVE-2026-73643.