Executive brief
Git for Windows, a Windows port of the popular version control system Git, is vulnerable to credential exposure when cloning or fetching from a malicious Git server. An attacker can craft a malicious bundle URI that forces Windows to initiate an SMB connection to an attacker-controlled server, causing the user's NTLM authentication credentials to be transmitted and captured. This exposure could lead to account compromise if the captured credentials are brute-forced.
Technical details
The vulnerability exists in Git for Windows' bundle URI handling code (bundle-uri.c), specifically in the functions transport_get_remote_bundle_uri(), fetch_bundle_uri_internal(), and copy_uri_to_file(). When transfer.bundleuri=true, a malicious remote Git server can advertise a bundle URI with a non-HTTP(S) protocol value (such as a UNC path or file:// URI targeting a network share). The code treats these as local filesystem paths and removes file URI prefixes, causing Windows to initiate an outbound SMB connection to the attacker-specified host. This triggers transparent NTLM authentication, exposing the user's NTLMv2 hash to the attacker. The fix restricts bundle URIs to protocols allowed by protocol.<name>.allow rules, excluding file:// URIs by default. This issue requires the user to perform a clone or fetch operation (no authentication required for the attacker-controlled Git server), and only manifests when transfer.bundleuri is enabled.
Affected products
- Git for Windows Git for Windows before 2.55.0.windows.4
Timeline
- 2026-08-21: disclosed
- 2026-08-11: patched: Git for Windows v2.55.0.windows.4 released