CVE-2021-27212: In OpenLDAP through 2.4.57 and 2.5.x through 2.5.1alpha, an assertion failure in slapd can occur in the issuer

Q: How do I fix CVE-2021-27212?

openldap: upgrade to newer than 2.4.57; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-27212 being exploited?

CVE-2021-27212 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-27212 affect?

CVE-2021-27212 affects openldap, debian linux. Severity is high (CVSS 7.5). 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 re

Q: How urgent is CVE-2021-27212?

Priority 66/100. High severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATE

CVE-2021-27212 is a high-severity flaw (CVSS 7.5) affecting openldap, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	66.1% (top 1%)
CISA exploited list	No
Weakness	CWE-617
Published	2021-02-14
Last modified	2026-10-14

Publisher (CNA): MITRE · Vendor: debian · openldap

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-02-14 03:15 UTCPublished CVE record published
2026-10-14 12:17 UTCUpdated Record last modified

openldap openldap UPGRADE

Affected: <= 2.4.57 · 2.5.0 alpha · 2.5.1 alpha

Fixed in: newer than 2.4.57

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy openldap || rpm -q openldap || openldap --version

2. UPGRADE to newer than 2.4.57 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade openldap

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade openldap

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

debian debian linux MITIGATE

Affected: 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-27212?

openldap: upgrade to newer than 2.4.57; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-27212 being exploited?

CVE-2021-27212 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-27212 affect?

CVE-2021-27212 affects openldap, debian linux. Severity is high (CVSS 7.5). 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 re

How urgent is CVE-2021-27212?

Priority 66/100. High severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · OpenLDAP vulnerabilities

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CVE-2020-36230 HIGH 7.5 UPGRADE MITIGATE A flaw was discovered in OpenLDAP before 2.4.57 leading in an assertion failure in slapd in the X.509 DN parsi
CVE-2020-36229 HIGH 7.5 UPGRADE MITIGATE A flaw was discovered in ldap_X509dn2bv in OpenLDAP before 2.4.57 leading to a slapd crash in the X.509 DN par
CVE-2020-36228 HIGH 7.5 UPGRADE MITIGATE An integer underflow was discovered in OpenLDAP before 2.4.57 leading to a slapd crash in the Certificate List

References

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