Unauthenticated RCE in Samba DCE/RPC SAMR check password script
CVE-2026-4408 is an unauthenticated remote code execution vulnerability in Samba’s DCE/RPC SAMR server logic related to password validation operations. The vulnerable path is reachable via the SAMR RPC methods SamValidatePasswordChange and SamValidatePasswordReset. In affected deployments, Samba invokes the configured "check password script" from smb.conf and, if that script uses the %u substitution character, a client-controlled username is inserted into the command line without proper escaping of shell metacharacters. This creates an OS command injection condition. The issue affects Samba file servers and classic non-AD domain controllers when samba-dcerpcd is started as a system service; the content also indicates the vulnerable path is reachable when "rpc start on demand helpers = no" is set. Active Directory Domain Controllers are not directly affected because they do not expand %u in this way.
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Exploits
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No public exploit code observed for this vulnerability.
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Recent activity
27 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical remote code execution vulnerability in the Samba DCE/RPC SAMR server caused by unsafe handling of client-supplied usernames passed to password check scripts when the %u substitution character is used under specific non-default configurations.
A remote command execution vulnerability in Samba caused by improper escaping of shell meta-characters in the "check password script" feature when configured with %u in certain non-standard deployments.
An unauthenticated remote code execution vulnerability in Samba's DCE/RPC SAMR server caused by passing a client-controlled username to the configured check password script without escaping shell metacharacters when %u is used.
A Samba command injection vulnerability in the SAMR DCE/RPC password validation path that can lead to remote code execution when specific external daemon and check password script configurations are enabled.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.