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CVE-2026-18503

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

LOW
2.4
CVSS Score
Published: August 10, 2026 at 01:45 PM UTC
Updated: October 23, 2026 at 08:10 PM UTC
1 product affected across 1 vendorPython

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Severity
LOW2.4
Exploit prediction
EPSS 0.1%
SSVC
No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Python· Python
90%
03.11.03.12.03.13.03.14.03.15.0a13.16.0a1
Affected range stops below 3.10.21, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.11.16, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.12.14, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.13.15, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.14.7, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.15.0rc1, so it looks safe — our inference, not a vendor statement

References (9)

Vendor Advisory
Source: cverecord
https://mail.python.org/archives/list/[email protected]/thread/KQ7NBMCPAZJHRROQXJQE4GMXGLD5KHBS/
Patch
Source: cverecord
https://github.com/python/cpython/pull/153694
Issue Tracking
Source: cverecord
https://github.com/python/cpython/issues/98820
Patch
Source: cverecord
https://github.com/python/cpython/commit/063d4555c94ef412c731527dbf30193327f2ee82
Patch
Source: cverecord
https://github.com/python/cpython/commit/476fb09cdb0d73e645849d98c610e7e5697ce7c9
Patch
Source: cverecord
https://github.com/python/cpython/commit/89f29c760c02774b099ddd6863268eb13fa3946a
Patch
Source: cverecord
https://github.com/python/cpython/commit/b30c7fa9edd921a118f286e9f90f560777fa693b
Patch
Source: cverecord
https://github.com/python/cpython/commit/b09a67a20c464f8288c9f9a6b9c7082a74560024

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

2.4LOWPSF
Vector?

Quick Info

StatusAWAITING ANALYSIS
CWE
CWE-1176

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