CVE-2026-18503 PUBLISHED

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().

• Serhiy Storchaka (https://github.com/serhiy-storchaka) remediation developer
• Jack Desert (https://github.com/jackdesert) reporter
• Sean Gilligan (https://github.com/sg3-141-592) reporter
• Seth Larson (https://github.com/sethmlarson) coordinator

• https://mail.python.org/archives/list/security-announce@python.org/thread/KQ7NBMCPAZJHRROQXJQE4GMXGLD5KHBS/
• https://github.com/python/cpython/pull/153694
• https://github.com/python/cpython/issues/98820
• 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

• CWE-1176 CWE