Search: nav-mail.hol.es

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.

Inefficient algorithmic complexity and a non-terminating loop in the MIME processing of received messages in Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote unauthenticated attacker to make the mail services unavailable by sending a message. Removing a MIME header parameter whose value is empty and directly followed by a semicolon (for example a Content-Disposition with 'filename=a.bat; filename=;') entered a loop that never terminates, holding a worker thread at full load until the server is restarted; this is reached when the attachment blocker renames a blocked attachment or a filename is set over the REST API. Separately, decoding a header field that holds many RFC 2047 encoded words of an encoding other than base64 or quoted-printable, removing a parameter with many RFC 2231 continuations, and deleting many header fields of one name each took time growing with the square of the message, on the small thread pools that serve IMAP, SMTP and POP3 connections, delivery and the REST API.

Inefficient 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.

Inefficient algorithmic complexity in the JSON reader of Progressive Robot hMailServer allows a remote unauthenticated attacker to make the mail services unavailable. Reading a JSON object kept the first of each duplicated member name by searching the members already read, so an object of N distinct member names cost O(N^2): 1 MB took 8.9 seconds and 4 MB took 300 seconds against the affected code. A remote attacker reaches the reader without an account by mailing a crafted TLS-RPT report (up to 16 MB after decompression) to a hosted domain's published report mailbox, which is read on a delivery thread; a few such reports hold every delivery thread (ten by default), so the server delivers no mail, local or outbound, for over an hour per report. A signed-in account reaches the same 16 MB body through the webmail's own REST routes, holding the REST API's own worker threads. Where no report mailbox is configured, the unauthenticated REST sign-in routes that read a JSON body are capped at 64 KB and are not affected.