CVE-2021-21439: Possible DoS attack using a special crafted URL in email body

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-14 · updated 2026-06-17
Weakness: CWE-754

Description

DoS attack can be performed when an email contains specially designed URL in the body. It can lead to the high CPU usage and cause low quality of service, or in extreme case bring the system to a halt. This issue affects: OTRS AG ((OTRS)) Community Edition 6.0.x version 6.0.1 and later versions. OTRS AG OTRS 7.0.x version 7.0.26 and prior versions; 8.0.x version 8.0.13 and prior versions.

Affected products

OTRS AG OTRS: from 6.0.1 through 6.0.30; from 7.0.0 before 7.0.27; from 8.0.0 before 8.0.14 — fixed in 7.0.27, 8.0.14

How to fix

Upgrade to a fixed version: OTRS AG OTRS 7.0.27, 8.0.14. Check the vendor advisory for mitigations.

References

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