CVE-2021-34555Network attack vector

Remote mail-filter crash via null domain comparison

Published Jun 10, 2021 · Updated Aug 4, 2024

NULL pointer dereference in OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to crash the mail filter with a crafted From header. The mlfi_eom function compares entries in its domains array with strcasecmp without first ensuring that each parsed From value contains a non-NULL domain. An unauthenticated sender must deliver a message with multiple From values, including one lacking a domain, which interrupts mail filtering until the process restarts.

CVSS severity7.5
High
EPSS probability2.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in OpenDMARC 1.4.1 and 1.4.1.1 allows remote attackers to crash the mail filter with a crafted From header. The mlfi_eom function compares entries in its domains array with strcasecmp without first ensuring that each parsed From value contains a non-NULL domain. An unauthenticated sender must deliver a message with multiple From values, including one lacking a domain, which interrupts mail filtering until the process restarts.

The record

CVE
CVE-2021-34555
Published
Jun 10, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 10, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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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