Fix quadratic-time PEM scanning in load_ssh_private_key - #15461
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load_ssh_private_key located the OpenSSH PEM block with a regex whose runtime is quadratic in the length of the input: re.search restarts at every occurrence of the opening marker and rescans to the end of the input looking for a closing marker, so input with an opening marker and no closing marker drives O(n^2) work before any parsing or size check. An attacker who can supply data to the function can consume unbounded CPU (~8s for 273 KiB, extrapolating to hours for a few MiB). Locate the markers directly with bytes.find instead. The first opening marker and the first closing marker after it delimit exactly what the lazy regex matched, and finding them is linear. memoryview inputs, which _check_byteslike permits but bytes.find does not, are converted first. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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load_ssh_private_key located the OpenSSH PEM block with a regex whose runtime is quadratic in the length of the input: re.search restarts at every occurrence of the opening marker and rescans to the end of the input looking for a closing marker, so input with an opening marker and no closing marker drives O(n^2) work before any parsing or size check. An attacker who can supply data to the function can consume unbounded CPU (~8s for 273 KiB, extrapolating to hours for a few MiB).
Locate the markers directly with bytes.find instead. The first opening marker and the first closing marker after it delimit exactly what the lazy regex matched, and finding them is linear. memoryview inputs, which _check_byteslike permits but bytes.find does not, are converted first.
Thanks to @jaypatrickhoward for reporting this.