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Vulnerability record · CVE-2021-27212 · published 14 February 2021

CVE-2021-27212: OpenLDAP slapd assertion failure in timestamp check causes DoS

Openldap · Openldap

OpenLDAP slapd through 2.4.57 and 2.5.x through 2.5.1alpha can hit an assertion failure in issuerAndThisUpdateCheck (schema_init.c, checkTime) when processing a crafted packet containing a short timestamp. The daemon exits, so a single malformed request can take down the directory service.

7.5 CVSS 3.1 High EPSS 64% · top 0.8% CWE-617 · CWE-617
7.5CVSS 3.1 base score, v2 5.0
64%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
16References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

In OpenLDAP through 2.4.57 and 2.5.x through 2.5.1alpha, an assertion failure in slapd can occur in the issuerAndThisUpdateCheck function via a crafted packet, resulting in a denial of service (daemon exit) via a short timestamp. This is related to schema_init.c and checkTime.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 19 September 2026. Confidence: high.

high priorityNetwork-reachable unauthenticated crash of a core directory service with high EPSS and public exploit references, though impact is limited to availability.

What it is

OpenLDAP slapd through 2.4.57 and 2.5.x through 2.5.1alpha can hit an assertion failure in issuerAndThisUpdateCheck (schema_init.c, checkTime) when processing a crafted packet containing a short timestamp. The daemon exits, so a single malformed request can take down the directory service.

Impact

An unauthenticated attacker can crash slapd, causing a denial of service and loss of LDAP authentication and directory services for all dependent applications.

Attack surface

Reachable over the network via a crafted packet to the LDAP service; the CVSS vector shows no privileges and no user interaction required.

Exploitation

Not listed in CISA KEV, but EPSS is 0.64147 (99.19th percentile) and the vendor bug report is tagged Exploit, indicating public exploit material exists.

What to do

  • Upgrade OpenLDAP to a release containing the fixes in commits 3539fc33 and 9badb734 (post-2.4.57 and post-2.5.1alpha).
  • Apply the Debian DSA-4860 or LTS updates if running packaged OpenLDAP.
  • Restrict network access to slapd ports to trusted clients only.
  • Monitor slapd process restarts and configure service supervision to auto-recover from daemon exits.

Detection

  • Alert on slapd process termination or unexpected restarts in systemd/journal logs.
  • Watch for assertion failure messages referencing issuerAndThisUpdateCheck, schema_init.c or checkTime.
  • Baseline and monitor LDAP request rates for malformed or anomalous packets from untrusted sources.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugs.openldap.org/show_bug.cgi?id=9454 ExploitIssue TrackingVendor Advisory
https://git.openldap.org/openldap/openldap/-/commit/3539fc33212b528c56b716584f2c2994af7c30b0 PatchVendor Advisory
https://git.openldap.org/openldap/openldap/-/commit/9badb73425a67768c09bcaed1a9c26c684af6c30 PatchVendor Advisory
https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.ap
https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.ap
https://lists.debian.org/debian-lts-announce/2021/02/msg00035.html Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210319-0005/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4860 Third Party Advisory
https://bugs.openldap.org/show_bug.cgi?id=9454 ExploitIssue TrackingVendor Advisory
https://git.openldap.org/openldap/openldap/-/commit/3539fc33212b528c56b716584f2c2994af7c30b0 PatchVendor Advisory
https://git.openldap.org/openldap/openldap/-/commit/9badb73425a67768c09bcaed1a9c26c684af6c30 PatchVendor Advisory
https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.ap
https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.ap
https://lists.debian.org/debian-lts-announce/2021/02/msg00035.html Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20210319-0005/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4860 Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-27212), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.