Git is a source code management tool. When cloning from a server (or fetching, or pushing), informational or error messages are transported from the remote Git process to the client via the so-called sideband channel. These messages will be prefixed with remote: and printed directly to the standard error output. Typically, this standard error output is connected to a terminal that understands ANSI escape sequences, which Git did not protect against. Most modern terminals support control sequences that can be used by a malicious actor to hide and misrepresent information, or to mislead the user into executing untrusted scripts. As requested on the git-security mailing list, the patches are under discussion on the public mailing list. Users are advised to update as soon as possible. Users unable to upgrade should avoid recursive clones unless they are from trusted sources.
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
Improper encoding or escaping can allow attackers to change the commands that are sent to another component, inserting malicious commands instead. Most products follow a certain protocol that uses structured messages for communication between components, such as queries or commands. These structured messages can contain raw data interspersed with metadata or control information. For example, “GET /index.html HTTP/1.1” is a structured message containing a command (“GET”) with a single argument ("/index.html") and metadata about which protocol version is being used (“HTTP/1.1”). If an application uses attacker-supplied inputs to construct a structured message without properly encoding or escaping, then the attacker could insert special characters that will cause the data to be interpreted as control information or metadata. Consequently, the component that receives the output will perform the wrong operations, or otherwise interpret the data incorrectly.