CVE-2026-67194

Description

Courier IMAP before 6.0.1 and Courier Mail Server before 2.0.2 allow authenticated IMAP users to crash the imapd process via deeply nested parenthesized SEARCH queries. The SEARCH command parser (alloc_search_key in searchinfo.C) recursively descends on nested parenthesized groups through a mutual recursion chain with alloc_search_andlist() and alloc_search_notkey(), with no depth limit. Courier IMAP has no overall command line length limit, making exploitation trivial. A single IMAP command with ~2500 nested parentheses overflows the 8MB default stack, causing SIGSEGV.

References

https://www.vulncheck.com/advisories/courier-imap-mail-server-stack-overflow-dos-via-nested-search-queries

https://packages.debian.org/sid/courier-imap

https://github.com/svarshavchik/courier/releases/tag/courier-imap%2F6.0.1%2F20260627214444

https://github.com/svarshavchik/courier/releases/tag/courier%2F2.0.2%2F20260627214309

https://github.com/svarshavchik/courier-libs/commit/b5b5581aabea3efadf5e2944947ff0214aa3533e

Details

Source: Mitre, NVD

Risk Information

CVSS v2

CVSS v3

CVSS v4