Progressive Robot hMailServer up to 6.3.5 IMAP Command Parser resource consumption

Summaryinfo

A vulnerability, which was classified as problematic, was found in Progressive Robot hMailServer up to 6.3.5. This affects an unknown part of the component IMAP Command Parser. Such manipulation leads to resource consumption. This vulnerability is referenced as CVE-2026-107581. It is possible to launch the attack remotely. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Progressive Robot hMailServer up to 6.3.5. It has been rated as problematic. Affected by this issue is some unknown functionality of the component IMAP Command Parser. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. CVE summarizes:

Progressive Robot hMailServer 6.0.0 through 6.3.5 processes several IMAP commands from a signed-in account in time quadratic in the command's length or in the number of elements it names, and can be made to hold memory out of proportion to a command. The FETCH data-item parser normalised a BODY[] section with a case-insensitive string replacement that copied the whole item per occurrence and split the item list by repeatedly copying the remainder of the command; the server's case-insensitive search compared a needle afresh at every position, so a long SEARCH TEXT key over a message cost the product of the two lengths; SEARCH message sets and the saved-result marker ($), SORT criteria, HEADER.FIELDS name lists and UID ranges were each read once per message rather than once per command; and a FETCH naming a message's sections very many times read and held every section in memory before sending any. An IMAP command may continue past one line through non-synchronizing literals, so one command can reach about eleven megabytes. The IMAP worker threads are a small pool shared with SMTP and POP3, so a signed-in user sending such commands can make the IMAP, SMTP and POP3 services stop responding (CWE-407) and can consume excessive memory (CWE-400).

The advisory is shared for download at gitlab.com. This vulnerability is handled as CVE-2026-107581 since 10/08/2026. The exploitation is known to be easy. The attack may be launched remotely. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 6.3.6 eliminates this vulnerability.

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Productinfo

Type

• Mail Server Software

Vendor

• Progressive Robot

Name

• hMailServer

Version

• 6.3.0
• 6.3.1
• 6.3.2
• 6.3.3
• 6.3.4
• 6.3.5

CPE 2.3info

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CPE 2.2info

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