CVE-2021-21439Network attack vector

Service halt via crafted email URL

Published Jun 14, 2021 · Updated Sep 16, 2024

Improper exception handling in OTRS 7.0.26 and earlier and 8.0.13 and earlier allows remote attackers to halt service via an email URL. OTRS AG has not disclosed the URL-processing component or exceptional condition that drives CPU use when an agent handles the message. An agent must interact with the crafted email; affected ((OTRS)) Community Edition releases start at 6.0.1, and sustained CPU use can halt the system.

CVSS severity6.5
Medium
EPSS probability0.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper exception handling in OTRS 7.0.26 and earlier and 8.0.13 and earlier allows remote attackers to halt service via an email URL. OTRS AG has not disclosed the URL-processing component or exceptional condition that drives CPU use when an agent handles the message. An agent must interact with the crafted email; affected ((OTRS)) Community Edition releases start at 6.0.1, and sustained CPU use can halt the system.

The record

CVE
CVE-2021-21439
Published
Jun 14, 2021
Updated
Sep 16, 2024
Vendor
OTRS AG
Product
OTRS
Classifications
CWE-754, CWE-755, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 14, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.0.x <=7.0.26
  2. Affected versionversion=8.0.x <=8.0.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OTRS AG · OTRSversion=7.0.x <=7.0.26; version=8.0.x <=8.0.13
OTRS AG · ((OTRS)) Community Editionversion=6.0.1 <6.0.x*

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
6.5OTRS AGCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

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-754Improper Check for Unusual or Exceptional Conditions
CWE-755Improper Handling of Exceptional Conditions
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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