---
id: CVE-2026-18503
title: |-
  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().
summary: |-
  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().
severity: low
cwe:
  - CWE-1176
published: '2026-08-10'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T01:17:06.473'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-18503'
references:
  - url: >-
      https://github.com/python/cpython/commit/063d4555c94ef412c731527dbf30193327f2ee82
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/476fb09cdb0d73e645849d98c610e7e5697ce7c9
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/89f29c760c02774b099ddd6863268eb13fa3946a
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/b09a67a20c464f8288c9f9a6b9c7082a74560024
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/b30c7fa9edd921a118f286e9f90f560777fa693b
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/fd78b565d7c326f96ae903ab945b47f35d829cf4
    label: cna@python.org
  - url: 'https://github.com/python/cpython/issues/98820'
    label: cna@python.org
  - url: 'https://github.com/python/cpython/pull/153694'
    label: cna@python.org
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/KQ7NBMCPAZJHRROQXJQE4GMXGLD5KHBS/
    label: cna@python.org
tags:
  - nvd
  - cve.org
epss: 0.00119
epssPercentile: 0.0177
ingestedAt: '2026-10-14T02:10:14.762Z'
vendor: Python Software Foundation
product: CPython
affected:
  - CPython < 3.10.21
  - CPython >= 3.11.0 < 3.11.16
  - CPython >= 3.12.0 < 3.12.14
  - CPython >= 3.13.0 < 3.13.15
  - CPython >= 3.14.0 < 3.14.7
  - CPython >= 3.15.0a1 < 3.15.0rc1
  - CPython >= 3.16.0a1 < 3.16.0
cvss: 2.4
cvssVector: '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'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-10T17:56:17.853221Z'
cvssSource: cna
---

## Overview

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().

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.