Vulnerabilidad · Publicado 08/10/2026
Una complejidad algorítmica ineficiente en la verificación de firmas DKIM y ARC en Progressive Robot hMailServer 6.0.0 a 6.3.5 permite a atacantes remotos no autenticados saturar servidores de correo mediante mensajes especialmente crafted. El procesamiento de encabezados crece exponencialmente, causando consumo excesivo de recursos y caída del servicio de correo, impactando directamente la comunicación empresarial en organizaciones que dependen de este servidor.
Inefficient algorithmic complexity in the inbound DKIM and ARC signature verification of Progressive Robot hMailServer 6.0.0 through 6.3.5 allows a remote unauthenticated attacker to make the mail services unavailable by sending a message. Building the canonical header and choosing the header fields named in a signature's h= tag took time growing with the square of the message's header: the 'simple' canonicalisation prepended each continuation line of a folded field to the lines already gathered, and both canonicalisations searched the gathered fields from the bottom for each h= name and erased the match from the middle of the list. A message whose header holds very many fields, or a field folded over very many lines, with a DKIM-Signature the attacker signs for a domain they control, keeps a worker thread busy for tens of seconds per signature; up to ten signatures are evaluated per message by each of the DKIM and DMARC tests, on the threads that serve delivery and SMTP.
Score: 7.5/10 — Severidad: HIGH — Estado NIST: Received
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE-407
Publicado en NIST NVD.