GHSA-jr96-gvgh-j3r4

### Impact 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. ### Patches This has been fixed in [pypdf==6.21.2](https://github.com/py-pdf/pypdf/releases/tag/6.21.2). ### Workarounds If you cannot upgrade yet, consider applying the changes from PR [#4240](https://github.com/py-pdf/pypdf/pull/4240). ### Notes 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.