CVE-2022-4891Public exploitNetwork attack vector

Processing hang via greedy HTML tag regexes

Published Jan 17, 2023 · Updated Aug 3, 2024

Regular-expression denial of service in Sisimai 4.25.14p11 and earlier allows attackers to hang processing with crafted HTML email bodies. Sisimai::String.to_plain applies greedy, dot-matches-newline head and style tag expressions that scan and backtrack across attacker-controlled HTML. Exposure depends on a consuming application passing untrusted HTML email bodies to to_plain; successful input causes excessive regex work and stalls message processing.

CVSS severity7.5
High
EPSS probability1.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular-expression denial of service in Sisimai 4.25.14p11 and earlier allows attackers to hang processing with crafted HTML email bodies. Sisimai::String.to_plain applies greedy, dot-matches-newline head and style tag expressions that scan and backtrack across attacker-controlled HTML. Exposure depends on a consuming application passing untrusted HTML email bodies to to_plain; successful input causes excessive regex work and stalls message processing.

The record

CVE
CVE-2022-4891
Published
Jan 17, 2023
Updated
Aug 3, 2024
Vendor
Sisimai
Product
Sisimai
Classifications
CWE-1333, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=4.25.14p11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Sisimai · Sisimaiversion=4.25.14p11

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
2.7VulDBAV:A/AC:L/Au:S/C:N/I:N/A:P
3.5VulDBCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
4.3GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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 exploitPublished

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.003Application Exhaustion Flood

Public exploit references

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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