CVE-2026-107575 Inefficient Algorithmic Complexity in hMailServer
Remote attackers can cause partial denial of service in hMailServer by publishing crafted SPF records that trigger inefficient algorithmic complexity during macro expansion.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-107575?
CVE-2026-107575 is a medium-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Inefficient algorithmic complexity in the SPF macro expansion of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to consume worker-thread time by publishing a crafted SPF record. RFC 7208 section 7.1 requires a name too long to look up to lose whole labels from the left; the server did this by removing one label at a time and copying the rest of the name each time, so the work grew with the square of the expansion. An attacker who publishes an SPF record for a domain they control, with a mechanism whose domain-spec expands through macros to a name far longer than 253 characters, makes the SPF check of a message from that domain take several seconds. The expansion is bounded by SPF's own per-term and per-macro limits, so the loss of availability is partial.
Weakness: CWE-407
Which versions are affected by CVE-2026-107575?
How do I fix CVE-2026-107575?
No fix has been published for CVE-2026-107575 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-2026-107575 being exploited?
There is no known exploitation of CVE-2026-107575 in the wild and no public exploit code.
Sources
Also known as GHSA-qcpx-92mh-q44f.