CVE-2021-36093Network attack vector

Email-processing denial of service via incorrect regex

Published Sep 6, 2021 · Updated Sep 16, 2024

Denial of service in OTRS and ((OTRS)) Community Edition allows remote attackers to stall PostMaster email processing. Affected releases are OTRS 7.0.x through 7.0.28, OTRS 8.0.x through 8.0.15, and Community Edition 6.0.1 and later in 6.0.x. Incorrect regular-expression handling while a PostMaster filter evaluates a crafted message leaves processing stuck; the exact expression is undisclosed, and the impact is limited to interrupted email handling.

CVSS severity5.3
Medium
EPSS probability1.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in OTRS and ((OTRS)) Community Edition allows remote attackers to stall PostMaster email processing. Affected releases are OTRS 7.0.x through 7.0.28, OTRS 8.0.x through 8.0.15, and Community Edition 6.0.1 and later in 6.0.x. Incorrect regular-expression handling while a PostMaster filter evaluates a crafted message leaves processing stuck; the exact expression is undisclosed, and the impact is limited to interrupted email handling.

The record

CVE
CVE-2021-36093
Published
Sep 6, 2021
Updated
Sep 16, 2024
Vendor
OTRS AG
Product
OTRS
Classifications
CWE-185, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 6, 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 <=7.0.28
  2. Affected versionversion=8.0.x <=8.0.15

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OTRS AG · OTRSversion=7.0.x <=7.0.28; version=8.0.x <=8.0.15
OTRS AG · ((OTRS)) Community Editionversion=6.0.1 <6.0.x*

Published CVSS scores

5.3OTRS AGCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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.

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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-185Incorrect Regular Expression
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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