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GHSA-9frc-8383-795m
No affected components available
Description
Symfony\Component\Yaml\Parser::cleanup() strips the optional %YAML directive header, leading comments, and document start/end markers before parsing. The original regexes contained overlapping quantifiers, most notably '#^%YAML[: ][\d.]+.*\n#u', whose [\d.]+ and .* overlap on the dot, that exhibit catastrophic backtracking on crafted input. A single oversized %YAML directive header (or comment / document-marker line) makes the parser hang for an arbitrarily long time, denying service.
Resolution
The four regexes in Parser::cleanup() (YAML directive header, leading comments, document-start marker, document-end marker) have been rewritten with possessive quantifiers and unambiguous character classes so backtracking cannot occur.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
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.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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