CVE-2026-18503

Description

Attacker-controlled CSV samples can trigger super-linear regular-expression work during dialect sniffing and consume significant CPU when applications pass unbounded input to csv.Sniffer.sniff().

References

• https://github.com/python/cpython/commit/063d4555c94ef412c731527dbf30193327f2ee82
• https://github.com/python/cpython/commit/476fb09cdb0d73e645849d98c610e7e5697ce7c9
• https://github.com/python/cpython/commit/89f29c760c02774b099ddd6863268eb13fa3946a
• https://github.com/python/cpython/commit/b30c7fa9edd921a118f286e9f90f560777fa693b
• https://github.com/python/cpython/issues/98820
• https://github.com/python/cpython/pull/153694
• https://mail.python.org/archives/list/security-announce@python.org/thread/KQ7NBMCPAZJHRROQXJQE4GMXGLD5KHBS/