What’s Vulnerable › Vulnerabilities

CVE-2026-18503: Super-linear CPU usage for unbounded input to csv.Sniffer.sniff()

• Severity: low (CVSS 2.4 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-10 · updated 2026-10-23
• Weakness: CWE-1176

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().

Affected products

• Python: before 3.10.21; from 3.11.0 before 3.11.16; from 3.12.0 before 3.12.14; from 3.13.0 before 3.13.15; from 3.14.0 before 3.14.7; from 3.15.0a1 before 3.15.0rc1 — fixed in 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7, 3.15.0rc1

How to fix

Upgrade to a fixed version: Python 3.10.21, 3.11.16, 3.12.14, 3.13.15. Check the vendor advisory for mitigations.

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/b09a67a20c464f8288c9f9a6b9c7082a74560024
• https://github.com/python/cpython/commit/b30c7fa9edd921a118f286e9f90f560777fa693b
• https://github.com/python/cpython/commit/fd78b565d7c326f96ae903ab945b47f35d829cf4
• 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/

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