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

> Authenticated users can crash the Courier IMAP server by sending deeply nested SEARCH queries, causing a stack overflow and service disruption.

- **Severity:** High 7.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 14 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-67194, GHSA-mcmr-g7gg-p242, UBUNTU-CVE-2026-67194

## What is CVE-2026-67194?

CVE-2026-67194 is a high-severity denial of service vulnerability in svarshavchik Courier IMAP, published on 29 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-67194?


## How do I fix CVE-2026-67194?

Upgrade to a fixed version.

## Is CVE-2026-67194 being exploited?

There is no known exploitation of CVE-2026-67194 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67194 and fix it if it is affected.

What it is: CVE-2026-67194 is a high-severity denial of service vulnerability in svarshavchik Courier IMAP, published on 29 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-67194 in the wild and no public exploit code.

Affected product: svarshavchik Courier IMAP. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-67194/ (Markdown: https://insights.sbomify.com/CVE-2026-67194/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67194
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67194
- OSV: https://osv.dev/vulnerability/CVE-2026-67194

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67194/
Summaries are generated and may contain mistakes; the official description above is the record.