FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

fetchmail -- STARTTLS denial of service

Affected packages
fetchmail < 6.3.20


VuXML ID f7d838f2-9039-11e0-a051-080027ef73ec
Discovery 2011-04-28
Entry 2011-06-06

Matthias Andree reports:

Fetchmail version 5.9.9 introduced STLS support for POP3, version 6.0.0 added STARTTLS for IMAP. However, the actual S(TART)TLS-initiated in-band SSL/TLS negotiation was not guarded by a timeout.

Depending on the operating system defaults as to TCP stream keepalive mode, fetchmail hangs in excess of one week after sending STARTTLS were observed if the connection failed without notifying the operating system, for instance, through network outages or hard server crashes.

A malicious server that does not respond, at the network level, after acknowledging fetchmail's STARTTLS or STLS request, can hold fetchmail in this protocol state, and thus render fetchmail unable to complete the poll, or proceed to the next server, effecting a denial of service.

SSL-wrapped mode on dedicated ports was unaffected by this problem, so can be used as a workaround.


CVE Name CVE-2011-1947