CVE-2026-107581 Inefficient Algorithmic Complexity in hMailServer
Authenticated users can cause denial of service in hMailServer by sending crafted IMAP commands that trigger inefficient algorithmic complexity and excessive memory consumption.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-107581?
CVE-2026-107581 is a medium-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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).
Weakness: CWE-407
Which versions are affected by CVE-2026-107581?
How do I fix CVE-2026-107581?
No fix has been published for CVE-2026-107581 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-107581 being exploited?
There is no known exploitation of CVE-2026-107581 in the wild and no public exploit code.
Sources
Also known as GHSA-45mp-xx9j-6p9v.