Inefficient Regular Expression Complexity in hMailServer

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-107572
StatePUBLISHED
AssignerGitLab
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-08 12:17:14 UTC
Updated2026-10-08 21:02:43 UTC
DescriptionInefficient complexity in the Sieve filter evaluation of Progressive Robot hMailServer 6.2.24 through 6.3.5 allows an authenticated account holder to make the mail services unavailable with their own filter. A ':matches' pattern was matched by a backtracking descent whose time grew with the matched value's length raised to the number of wildcards, so a pattern such as '*a*a*a*b' over 800 characters took 44 seconds; and 'deleteheader' erased the fields it removed one at a time, so removing many fields of one name over a message's header cost O(N^2) (80,000 fields took 18.8 seconds). Sieve filters run on the small, shared delivery thread pool, so an account holder whose active script does this, fed a few messages they can send themselves, empties the pool and stops delivery for the whole server. The script is the account holder's own and cannot be set for another user.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.003070000 probability, percentile 0.215990000 (date 2026-10-10)

Problem Types: CWE-1333 | CWE-1333 CWE-1333: Inefficient Regular Expression Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1CNACVSS6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Progressive Robot Ltd HMailServer affected 6.2.24 6.3.6 semver Not specified

References

ReferenceSourceLinkTags
gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 [email protected] gitlab.com
gitlab.com/hmailserver/hmailserver/-/work_items/75 [email protected] gitlab.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Found in the hMailServer project's own security review (Progressive Robot Ltd) (en)

Additional Advisory Data

Solutions

CNA: Upgrade to hMailServer 6.3.6, which matches a ':matches' pattern by placing each piece once (time linear in the value times the pattern) and removes 'deleteheader' fields in one pass. Until then, review active Sieve scripts for ':matches' patterns with several wildcards and for 'deleteheader', and lower the maximum message size.

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