CVE-2021-34555: OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to cause a denial of service (NULL pointer dereference and

This week

HIGH 7.5REMOTEDOWNGRADEMITIGATE

CVE-2021-34555 is a high-severity flaw (CVSS 7.5) affecting opendmarc, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a multi-value From header field.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.7% (top 14%)
CISA exploited list	No
Weakness	CWE-476
Published	2021-06-10
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fedoraproject · trusteddomain

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-06-10 15:15 UTCPublished CVE record published
2026-06-17 03:56 UTCUpdated Record last modified

trusteddomain opendmarc DOWNGRADE

Affected: 1.4.1 · 1.4.1.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.4.1

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.4.1 (Debian / Ubuntu)

apt-cache madison opendmarc sudo apt install opendmarc=<VERSION_BEFORE_1.4.1> sudo apt-mark hold opendmarc

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list opendmarc sudo dnf downgrade opendmarc-<VERSION_BEFORE_1.4.1> sudo dnf versionlock add opendmarc

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

fedoraproject fedora MITIGATE

Affected: 33 · 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

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-2021-34555?

opendmarc: downgrade or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-34555 being exploited?

CVE-2021-34555 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-2021-34555 affect?

CVE-2021-34555 affects opendmarc, fedora. Severity is high (CVSS 7.5). OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a multi-value From header field.

How urgent is CVE-2021-34555?

Priority 58/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2024-25768 HIGH 7.5 DOWNGRADE OpenDMARC 1.4.2 contains a null pointer dereference vulnerability in /OpenDMARC/libopendmarc/opendmarc_policy.
CVE-2020-12460 CRITICAL 9.8 UPGRADE MITIGATE OpenDMARC through 1.3.2 and 1.4.x through 1.4.0-Beta1 has improper null termination in the function opendmarc_
CVE-2020-12272 MEDIUM 5.3 UPGRADE MITIGATE OpenDMARC through 1.3.2 and 1.4.x allows attacks that inject authentication results to provide false informati
CVE-2019-20790 CRITICAL 9.8 UPGRADE DOWNGRADE OpenDMARC through 1.3.2 and 1.4.x, when used with pypolicyd-spf 2.0.2, allows attacks that bypass SPF and DMAR

References

← Back to latest CVEs