CVE-2020-36221: An integer underflow was discovered in OpenLDAP before 2.4.57 leading to slapd crashes in the Certificate Exac

Q: How do I fix CVE-2020-36221?

openldap: upgrade to 2.4.57; debian linux: mitigate or apply the listed mitigation; mac os x: upgrade to 10.14.6. Exact commands for each OS are on this page.

Q: Is CVE-2020-36221 being exploited?

CVE-2020-36221 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-2020-36221 affect?

CVE-2020-36221 affects openldap, debian linux, mac os x. Severity is high (CVSS 7.5). An integer underflow was discovered in OpenLDAP before 2.4.57 leading to slapd crashes in the Certificate Exact Assertion processing, resulting in denial of service (schema_init.c serialNumberAndIssuerCheck).

Q: How urgent is CVE-2020-36221?

Priority 61/100. High severity; EPSS top 1%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

This week

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATEUPGRADE

CVE-2020-36221 is a high-severity flaw (CVSS 7.5) affecting openldap, debian linux, mac os x. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An integer underflow was discovered in OpenLDAP before 2.4.57 leading to slapd crashes in the Certificate Exact Assertion processing, resulting in denial of service (schema_init.c serialNumberAndIssuerCheck).

Why this priority

High severity
EPSS top 1%: very likely to be exploited
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	85.0% (top 1%)
CISA exploited list	No
Weakness	CWE-191
Published	2021-01-26
Last modified	2026-10-14

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

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

Am I affected?

Timeline

2021-01-26 18:15 UTCPublished CVE record published
2026-10-14 10:17 UTCUpdated Record last modified

openldap openldap UPGRADE

Affected: < 2.4.57

Fixed in: 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 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.

apple mac os x UPGRADE

Affected: >= 10.14.0 and < 10.14.6 · 10.14.6 · 10.14.6 security_update_2019-004 · 10.14.6 security_update_2019-005 · 10.14.6 security_update_2019-006 · 10.14.6 security_update_2019-007 · 10.14.6 security_update_2020-001 · 10.14.6 security_update_2020-002

Fixed in: 10.14.6

Safe to downgrade to: a release before 10.14.0

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.

apple macos UPGRADE

Affected: >= 11.1 and < 11.4

Fixed in: 11.4

Safe to downgrade to: a release before 11.1

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-2020-36221?

openldap: upgrade to 2.4.57; debian linux: mitigate or apply the listed mitigation; mac os x: upgrade to 10.14.6. Exact commands for each OS are on this page.

Is CVE-2020-36221 being exploited?

CVE-2020-36221 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-2020-36221 affect?

CVE-2020-36221 affects openldap, debian linux, mac os x. Severity is high (CVSS 7.5). An integer underflow was discovered in OpenLDAP before 2.4.57 leading to slapd crashes in the Certificate Exact Assertion processing, resulting in denial of service (schema_init.c serialNumberAndIssuerCheck).

How urgent is CVE-2020-36221?

Priority 61/100. High severity; EPSS top 1%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · macOS vulnerabilities · OpenLDAP vulnerabilities

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References

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