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GHSA-pm4m-ph32-ghv5
No affected components available
Summary
Parsing a small YAML document can take exponential time. An application that calls load() or loadAll() on untrusted input can be hung by a payload under 200 bytes.
Details
When an entry in a flow sequence turns out to be a key: value pair, the parser rewinds and parses that entry a second time as the key.
If the key is itself a nested flow sequence of the same shape, every level is parsed twice, so the total work is O(2^n) in the nesting depth. The default maxDepth of 100 does not help, because the time is already unmanageable at about 30 to 40 levels.
Root cause, potentially the: readFlowCollection in parser.ts, the restoreState followed by a second parseNode further down.
PoC
const yaml = require('js-yaml')
const n = 30
yaml.load('[ '.repeat(n) + '1' + ' ]: 0'.repeat(n))
With default options: 22 levels takes about 1 second, 26 levels about 17 seconds, 30 levels over 2 minutes. The input stays under 200 bytes and grows linearly with n.
Impact
Denial of service. A single small request can keep one CPU busy for minutes or longer and blocks the Node event loop, so one request can stall the whole process. No anchors, aliases, merges, tags, or non default options are required, and it reproduces on the default schema.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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