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Fencer Vulns
medium 6.5

CVE-2021-46823 json

ReDoS in LDAP schema parser

published 2021-11-29 4 y ago modified 2026-07-08 4 mo ago also GHSA-qfr5-wjpw-q4c4 , GHSA-r8wq-qrxc-hmcm , PYSEC-2026-912 , EUVD-2022-6131

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.0%
EPSS 2.0% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

python-ldap before 3.4.0 is vulnerable to a denial of service when ldap.schema is used for untrusted schema definitions, because of a regular expression denial of service (ReDoS) flaw in the LDAP schema parser. By sending crafted regex input, a remote authenticated attacker could exploit this vulnerability to cause a denial of service condition.

Patch / fix

  • pypi python-ldap 3.4.0
  • python-ldap python-ldap 3.4.0
  • python-ldap Debian 14, Debian 13, Debian 12 3.4.0-1

debian advisories DEBIAN-CVE-2021-46823

  • python-ldap Ubuntu 18.04 LTS 3.0.0-1ubuntu0.2
  • python-ldap Ubuntu 20.04 LTS 3.2.0-4ubuntu2.1
  • python-ldap Ubuntu 22.04 LTS 3.2.0-4ubuntu7.1

ubuntu advisories UBUNTU-CVE-2021-46823

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-ldap CBL-Mariner 2.0 3.4.0-1

azure linux advisories AZL-9960

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2021-46823 updated cvss 6.5

python-ldap: Regular expression denial of service in LDAP schema parser

  • Red Hat Ansible Automation Platform 1.2 python-ldap Red Hat Ansible Tower 3 python-ldap Red Hat Enterprise Linux 6 python-ldap Red Hat Enterprise Linux 7 python-ldap Red Hat Enterprise Linux 8 python3-ldap Red Hat Enterprise Linux 9 python3-ldap
    +1 more products
    Red Hat OpenStack Platform 13 (Queens) python2-ldap3
    affected: workaround, no fix planned “Check input for an excessive amount of backslashes in schemas. More than a dozen backslashes per line are atypical.”
  • Red Hat Quay 3 quay/quay-rhel8
    affected: workaround, no fix available “Check input for an excessive amount of backslashes in schemas. More than a dozen backslashes per line are atypical.”
  • Red Hat OpenStack Platform 16.1 python3-ldap3 Red Hat OpenStack Platform 16.2 python3-ldap3
    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

Exploit prediction

1.97% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi python-ldap
<3.4.0
3.4.0

Classification

Weakness
  • CWE-1333 Inefficient Regular Expression Complexity

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.