Description

Git for Windows is the Windows port of Git. Prior to 2.55.0.windows.4, a malicious remote Git server can advertise a bundle URI that reaches transport_get_remote_bundle_uri(), fetch_bundle_uri_internal(), and copy_uri_to_file() in bundle-uri.c during clone or fetch when transfer.bundleuri=true. Non-HTTP(S) values are treated as local filesystem paths, and file URI prefixes are removed, so a bare UNC path or file URI targeting an attacker-controlled share causes Windows to initiate an outbound SMB connection. This can expose NTLM authentication material to the attacker-selected host. This issue is fixed in version 2.55.0.windows.4.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.4",
  "pubDate": "2026-08-21T20:16:38.700Z",
  "pubdate": "2026-08-21T20:16:38.700Z",
  "executiveSummary": "Git for Windows prior to version 2.55.0.windows.4 is susceptible to an NTLM authentication material disclosure vulnerability stemming from insecure handling of bundle URI inputs during clone and fetch operations when the transfer.bundleuri configuration is enabled.\nA malicious remote Git server can exploit this flaw by advertising crafted bundle URIs that are incorrectly interpreted as local filesystem paths or Windows UNC paths, causing the underlying Windows operating system to initiate automated outbound SMB connections to an attacker-controlled share.\nThis behavior results in the leakage of sensitive NTLM authentication material to the remote host, presenting significant risks of credential theft and subsequent relay attacks.\nThe attack capability requires a victim to interact with a malicious remote Git server, specifically executing a clone or fetch command while bundle URI transfers are enabled.\nImpacted systems include all Git for Windows deployments prior to the patched version 2.55.0.windows.4.",
  "technicalDetails": "The vulnerability resides within the bundle-uri.c component of Git for Windows, specifically affecting the functions transport_get_remote_bundle_uri(), fetch_bundle_uri_internal(), and copy_uri_to_file().\nThe root cause is the improper validation and sanitization of bundle URIs advertised by remote Git servers during git clone or git fetch operations when the configuration transfer.bundleuri=true is set.\nNon-HTTP(S) scheme values provided in the bundle URI advertisements are improperly handled and treated as local filesystem paths.\nAdditionally, file URI prefixes are systematically removed during parsing, allowing bare UNC paths or modified file URIs pointing to remote resources to bypass expected protocol restrictions.\nWhen a victim connects to a malicious remote Git server, the server advertises a crafted bundle URI targeting an attacker-controlled SMB share.\nUpon processing this URI, copy_uri_to_file() attempts to access the specified destination as a local or UNC path.\nThis action forces the Windows operating system to automatically initiate an outbound SMB connection to the attacker-selected host.\nDuring the establishment of the SMB connection, Windows transparently attempts authentication, exposing the user's NTLM authentication material (such as password hashes) to the remote attacker.\nExploitation requires no special privileges or authentication beyond the victim initiating a standard Git clone or fetch operation against a malicious or compromised remote repository where bundle URI transfers are enabled.\nThe affected product is Git for Windows in versions prior to 2.55.0.windows.4, and the post-exploitation impact includes potential credential theft, session hijacking, and NTLM relay attacks against internal network resources."
}