CVE-2021-46823Network attack vector

Service interruption via schema tokenizer regex backtracking

Published Jun 18, 2022 · Updated Aug 4, 2024

Regular expression denial of service in python-ldap before 3.4.0 allows remote authenticated users to interrupt LDAP schema parsing. The quoted-string regex in Lib/ldap/schema/tokenizer.py matches doubled backslashes through overlapping alternatives, causing excessive backtracking. Exposure requires an application to pass an untrusted LDAP schema definition to ldap.schema; CPU exhaustion then stalls the consuming service.

CVSS severity6.5
Medium
EPSS probability1.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in python-ldap before 3.4.0 allows remote authenticated users to interrupt LDAP schema parsing. The quoted-string regex in Lib/ldap/schema/tokenizer.py matches doubled backslashes through overlapping alternatives, causing excessive backtracking. Exposure requires an application to pass an untrusted LDAP schema definition to ldap.schema; CPU exhaustion then stalls the consuming service.

The record

CVE
CVE-2021-46823
Published
Jun 18, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1333, CWE-185, CWE-407, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 18, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5GitHubCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
CWE-185Incorrect Regular Expression
CWE-407Inefficient Algorithmic Complexity
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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