An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires cross-reference streams with repeated malformed cross-reference streams.
This has been fixed in pypdf==6.21.2.
If you cannot upgrade yet, consider applying the changes from PR #4240.
This is a follow-up to https://github.com/py-pdf/pypdf/security/advisories/GHSA-55h5-xmcq-c37v, which had the side-effect of still loading the whole stream again despite the cache being present.
{
"cwe_ids": [
"CWE-400",
"CWE-407"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-23T20:54:27Z",
"nvd_published_at": null,
"severity": "HIGH"
}