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| author | Johannes Schindelin <johannes.schindelin@gmx.de> | 2022-11-23 09:31:06 +0100 |
|---|---|---|
| committer | Pratyush Yadav <me@yadavpratyush.com> | 2023-01-24 14:10:40 +0100 |
| commit | aae9560a355d4ab91385e49eae62fade2ddd27ef (patch) | |
| tree | 228fd4a009b394c0c28a0320c79ba6965748dba9 | |
| parent | fd477a1d3bab580c2fcdc435f551dca3094286ae (diff) | |
| download | git-aae9560a355d4ab91385e49eae62fade2ddd27ef.tar.gz | |
Work around Tcl's default `PATH` lookup
As per https://www.tcl.tk/man/tcl8.6/TclCmd/exec.html#M23, Tcl's `exec`
function goes out of its way to imitate the highly dangerous path lookup
of `cmd.exe`, but _of course_ only on Windows:
If a directory name was not specified as part of the application
name, the following directories are automatically searched in
order when attempting to locate the application:
The directory from which the Tcl executable was loaded.
The current directory.
The Windows 32-bit system directory.
The Windows home directory.
The directories listed in the path.
The dangerous part is the second item, of course: `exec` _prefers_
executables in the current directory to those that are actually in the
`PATH`.
It is almost as if people wanted to Windows users vulnerable,
specifically.
To avoid that, Git GUI already has the `_which` function that does not
imitate that dangerous practice when looking up executables in the
search path.
However, Git GUI currently fails to use that function e.g. when trying to
execute `aspell` for spell checking.
That is not only dangerous but combined with Tcl's unfortunate default
behavior and with the fact that Git GUI tries to spell-check a
repository just after cloning, leads to a critical Remote Code Execution
vulnerability.
Let's override both `exec` and `open` to always use `_which` instead of
letting Tcl perform the path lookup, to prevent this attack vector.
This addresses CVE-2022-41953.
For more details, see
https://github.com/git-for-windows/git/security/advisories/GHSA-v4px-mx59-w99c
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>
| -rwxr-xr-x | git-gui.sh | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/git-gui.sh b/git-gui.sh index b0eb5a6ae4..cb92bba1c4 100755 --- a/git-gui.sh +++ b/git-gui.sh @@ -121,6 +121,62 @@ proc _which {what args} { return {} } +proc sanitize_command_line {command_line from_index} { + set i $from_index + while {$i < [llength $command_line]} { + set cmd [lindex $command_line $i] + if {[file pathtype $cmd] ne "absolute"} { + set fullpath [_which $cmd] + if {$fullpath eq ""} { + throw {NOT-FOUND} "$cmd not found in PATH" + } + lset command_line $i $fullpath + } + + # handle piped commands, e.g. `exec A | B` + for {incr i} {$i < [llength $command_line]} {incr i} { + if {[lindex $command_line $i] eq "|"} { + incr i + break + } + } + } + return $command_line +} + +# Override `exec` to avoid unsafe PATH lookup + +rename exec real_exec + +proc exec {args} { + # skip options + for {set i 0} {$i < [llength $args]} {incr i} { + set arg [lindex $args $i] + if {$arg eq "--"} { + incr i + break + } + if {[string range $arg 0 0] ne "-"} { + break + } + } + set args [sanitize_command_line $args $i] + uplevel 1 real_exec $args +} + +# Override `open` to avoid unsafe PATH lookup + +rename open real_open + +proc open {args} { + set arg0 [lindex $args 0] + if {[string range $arg0 0 0] eq "|"} { + set command_line [string trim [string range $arg0 1 end]] + lset args 0 "| [sanitize_command_line $command_line 0]" + } + uplevel 1 real_open $args +} + ###################################################################### ## ## locate our library |