CVE-2021-40110Network attack vector

Service interruption via backtracking mailbox-name regex

Published Jan 4, 2022 · Updated Aug 4, 2024

Regular expression denial of service in Apache James Server 3.6.0 and earlier allows remote authenticated users to hang IMAP processing. The IMAP LIST path builds a PrefixedRegex from attacker-controlled mailbox-pattern input and evaluates it with Java's backtracking regex engine, causing excessive computation. An account with IMAP access and network reachability is required; a crafted LIST request can consume processing time and interrupt mailbox service.

CVSS severity7.5
High
EPSS probability2.86%
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 Apache James Server 3.6.0 and earlier allows remote authenticated users to hang IMAP processing. The IMAP LIST path builds a PrefixedRegex from attacker-controlled mailbox-pattern input and evaluates it with Java's backtracking regex engine, causing excessive computation. An account with IMAP access and network reachability is required; a crafted LIST request can consume processing time and interrupt mailbox service.

The record

CVE
CVE-2021-40110
Published
Jan 4, 2022
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache James Server
Classifications
T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 4, 2022CVE 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?

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

  1. Affected versionversion=Apache James <=3.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

The Apache Software Foundation · Apache James Serverversion=Apache James <=3.6.0

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application 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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