CVE-2020-25709Public exploitNetwork attack vector

Service crash via malformed Certificate List syntax

Published May 18, 2021 · Updated Aug 4, 2024

Reachable assertion in OpenLDAP Software before 2.4.56 allows remote attackers to crash slapd with a malformed LDAP modify request. certificateListValidate in servers/slapd/schema_init.c asserts that a BER tag is LBER_INTEGER instead of rejecting invalid Certificate List syntax. No authentication or user interaction is required; a crafted packet reaching slapd aborts the process and interrupts directory service.

CVSS severity7.5
High
EPSS probability2.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in OpenLDAP Software before 2.4.56 allows remote attackers to crash slapd with a malformed LDAP modify request. certificateListValidate in servers/slapd/schema_init.c asserts that a BER tag is LBER_INTEGER instead of rejecting invalid Certificate List syntax. No authentication or user interaction is required; a crafted packet reaching slapd aborts the process and interrupts directory service.

The record

CVE
CVE-2020-25709
Published
May 18, 2021
Updated
Aug 4, 2024
Vendor
OpenLDAP Foundation
Product
OpenLDAP Software
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 18, 2021CVE 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=openldap 2.4.56

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenLDAP Foundation · OpenLDAP Softwareversion=openldap 2.4.56

Published CVSS scores

5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

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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