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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
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 | 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 include 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
Sources
Also known as GHSA-5835-4gvc-32pc, GO-2026-5137.