# CVE-2026-40193: Maddy Mail Server: LDAP Filter Injection via Unsanitized Username

> Attackers can inject LDAP filters via usernames to spoof identities, enumerate directories, and extract data from the Maddy Mail Server.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Apr 2026
- **Updated:** 16 Apr 2026
- **Also known as:** GHSA-5835-4gvc-32pc, GO-2026-5137

## What is CVE-2026-40193?

CVE-2026-40193 is a high-severity vulnerability in foxcpp maddy, published on 15 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

maddy is a composable, all-in-one mail server. Versions prior to 0.9.3 contain an LDAP injection vulnerability in the auth.ldap module where user-supplied usernames are interpolated into LDAP search filters and DN strings via strings.ReplaceAll() without any LDAP filter escaping, despite the go-ldap/ldap/v3 library's ldap.EscapeFilter() function being available in the same import. This affects three code paths: the Lookup() filter, the AuthPlain() DN template, and the AuthPlain() filter. An attacker with network access to the SMTP submission or IMAP interface can inject arbitrary LDAP filter expressions through the username field in AUTH PLAIN or LOGIN commands. This enables identity spoofing by manipulating filter results to authenticate as another user, LDAP directory enumeration via wildcard filters, and blind extraction of LDAP attribute values using authentication responses as a boolean oracle or via timing side-channels between the two distinct failure paths. This issue has been fixed in version 0.9.3.

Weakness: CWE-90 (Improper Neutralization of Special Elements used in an LDAP Query)

## Which versions are affected by CVE-2026-40193?

3 open source packages ship an affected version, including github.com/foxcpp/maddy. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/foxcpp/maddy` | Go | All versions | 0.9.3 |
| `github.com/foxcpp/maddy` | Go | All versions | 0.9.3 |
| `github.com/foxcpp/maddy` | Go | All versions | 0.9.3 |

Products: Maddy Project Maddy.

## How do I fix CVE-2026-40193?

Upgrade github.com/foxcpp/maddy to 0.9.3 or later.

## Is CVE-2026-40193 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40193 exists.

## Other vulnerabilities in foxcpp maddy

- [CVE-2023-27582](https://insights.sbomify.com/CVE-2023-27582/): Full authentication bypass if SASL authorization username is specified (critical 9.1)
- [CVE-2022-24732](https://insights.sbomify.com/CVE-2022-24732/): Maddy Mail Server does not implement account expiry (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40193 and fix it if it is affected.

What it is: CVE-2026-40193 is a high-severity vulnerability in foxcpp maddy, published on 15 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40193 exists.

Affected packages and fixed versions:
- github.com/foxcpp/maddy (Go): affected all versions; fixed in 0.9.3
- github.com/foxcpp/maddy (Go): affected all versions; fixed in 0.9.3
- github.com/foxcpp/maddy (Go): affected all versions; fixed in 0.9.3

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-2026-40193/ (Markdown: https://insights.sbomify.com/CVE-2026-40193/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40193
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40193
- OSV: https://osv.dev/vulnerability/CVE-2026-40193

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40193/
Summaries are generated and may contain mistakes; the official description above is the record.