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Vulnerability · Published Aug 10, 2026 · Assigned by PSF

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

Low 2.4

In plain English

A low-severity security flaw in CPython from Python Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 2% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)2.4Low
Exploit odds (30 days)0.1%top 98.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12pypy3no fix listedDEBIAN-CVE-2026-18503
Debian:13pypy3no fix listedDEBIAN-CVE-2026-18503
Debian:14pypy38.0.1+dfsg-1DEBIAN-CVE-2026-18503
Debian:12python3.113.11.2-6+deb12u9DEBIAN-CVE-2026-18503
Debian:13python3.13no fix listedDEBIAN-CVE-2026-18503
Debian:14python3.143.14.7-1DEBIAN-CVE-2026-18503
Debian:14python3.153.15.0~rc1-1DEBIAN-CVE-2026-18503
Ubuntu:22.04:LTSpython3.10no fix listedUBUNTU-CVE-2026-18503
Ubuntu:24.04:LTSpython3.12no fix listedUBUNTU-CVE-2026-18503
Ubuntu:26.04:LTSpython3.14no fix listedUBUNTU-CVE-2026-18503
Ubuntu:26.10python3.14no fix listedUBUNTU-CVE-2026-18503

Affected products (as reported)

VendorProductVersions
Python Software Foundation CPython 0 – before 3.10.213.11.0 – before 3.11.163.12.0 – before 3.12.143.13.0 – before 3.13.153.14.0 – before 3.14.73.15.0a1 – before 3.15.0rc13.16.0a1 – before 3.16.0

Weakness: CWE-1176 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References