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Fencer Vulns
high 7.5

CVE-2020-6817 json

regular expression denial-of-service (ReDoS) in Bleach

published 2020-03-30 6 y ago modified 2026-09-10 1 mo ago also GHSA-vqhp-cxgc-6wmm , PYSEC-2020-340 , EUVD-2020-0056

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits
0
none known

Summary

bleach.clean behavior parsing style attributes could result in a regular expression denial of service (ReDoS). Calls to bleach.clean with an allowed tag with an allowed style attribute are vulnerable to ReDoS. For example, bleach.clean(..., attributes={'a': ['style']}).

Patch / fix

  • pypi bleach 3.1.4
  • Mozilla Mozilla Bleach 3.1.4
  • python-bleach Debian 14, Debian 13, Debian 12 3.1.4-1

debian advisories DEBIAN-CVE-2020-6817

  • python-bleach Ubuntu Pro 16.04 LTS 1.4.2-1ubuntu0.1~esm1
  • python-bleach Ubuntu Pro 18.04 LTS 2.1.2-1ubuntu0.1~esm1
  • python-bleach Ubuntu Pro 20.04 LTS 3.1.1-1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2020-6817

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-bleach openSUSE Tumbleweed 6.4.0-1.1
  • python-bleach openSUSE Tumbleweed 6.1.0-1.5
  • python-bleach Package Hub 15 SP2 3.1.5-bp152.2.4.1
  • python-bleach openSUSE Leap 15.2 3.1.5-lp152.2.3.1

opensuse advisories openSUSE-SU-2026:11323-1openSUSE-SU-2024:14134-1openSUSE-SU-2021:0571-1openSUSE-SU-2021:0552-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-6817 updated cvss 5.9

python-bleach: behavior parsing style attributes could result in a regular expression denial of service (ReDoS)

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
19 mo ago

Exploit prediction

0.72% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1623633 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi bleach
<3.1.4
3.1.4

Affected products

  • Mozilla Mozilla Bleach

Classification

Weakness
  • CWE-1333 Inefficient Regular Expression Complexity
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.