CVE-2014-9938 (published 2017-03-20T00:59Z)

contrib/completion/git-prompt.sh in Git before 1.9.3 does not sanitize branch names in the PS1 variable, allowing a malicious repository to cause code execution.

Severity: MEDIUM
CVSS v2 base score: 6.8 (AV:N/AC:M/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 8.8, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-116
cwe_name: Improper Encoding or Escaping of Output
description: 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.
extended_description: 
            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.
         
         

Fix information:
repo_url: https://github.com/git/git
commit_details: repo_url: https://github.com/git/git
author: Richard Hansen
author_date: 2014-04-21 19:53:09-04:00
msg: git-prompt.sh: don't put unsanitized branch names in $PS1

Both bash and zsh subject the value of PS1 to parameter expansion,
command substitution, and arithmetic expansion.  Rather than include
the raw, unescaped branch name in PS1 when running in two- or
three-argument mode, construct PS1 to reference a variable that holds
the branch name.  Because the shells do not recursively expand, this
avoids arbitrary code execution by specially-crafted branch names such
as '$(IFS=_;cmd=sudo_rm_-rf_/;$cmd)'.

Signed-off-by: Richard Hansen <rhansen@bbn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
repository: repo_url: https://github.com/git/git
repo_name: git/git
description: Git Source Code Mirror - This is a publish-only repository but pull requests can be turned into patches to the mailing list via GitGitGadget (https://gitgitgadget.github.io/). Please follow Documentation/SubmittingPatches procedure for any of your improvements.
repo_language: C
owner: git
file_changes: filename: git-prompt.sh
change_type: ModificationType.MODIFY
diff: @@ -207,7 +207,18 @@ __git_ps1_show_upstream ()
 			p=" u+${count#*	}-${count%	*}" ;;
 		esac
 		if [[ -n "$count" && -n "$name" ]]; then
-			p="$p $(git rev-parse --abbrev-ref "$upstream" 2>/dev/null)"
+			__git_ps1_upstream_name=$(git rev-parse \
+				--abbrev-ref "$upstream" 2>/dev/null)
+			if [ $pcmode = yes ]; then
+				# see the comments around the
+				# __git_ps1_branch_name variable below
+				p="$p \${__git_ps1_upstream_name}"
+			else
+				p="$p ${__git_ps1_upstream_name}"
+				# not needed anymore; keep user's
+				# environment clean
+				unset __git_ps1_upstream_name
+			fi
 		fi
 	fi
 
@@ -438,8 +449,27 @@ __git_ps1 ()
 		__git_ps1_colorize_gitstring
 	fi
 
+	b=${b##refs/heads/}
+	if [ $pcmode = yes ]; then
+		# In pcmode (and only pcmode) the contents of
+		# $gitstring are subject to expansion by the shell.
+		# Avoid putting the raw ref name in the prompt to
+		# protect the user from arbitrary code execution via
+		# specially crafted ref names (e.g., a ref named
+		# '$(IFS=_;cmd=sudo_rm_-rf_/;$cmd)' would execute
+		# 'sudo rm -rf /' when the prompt is drawn).  Instead,
+		# put the ref name in a new global variable (in the
+		# __git_ps1_* namespace to avoid colliding with the
+		# user's environment) and reference that variable from
+		# PS1.
+		__git_ps1_branch_name=$b
+		# note that the $ is escaped -- the variable will be
+		# expanded later (when it's time to draw the prompt)
+		b="\${__git_ps1_branch_name}"
+	fi
+
 	local f="$w$i$s$u"
-	local gitstring="$c${b##refs/heads/}${f:+$z$f}$r$p"
+	local gitstring="$c$b${f:+$z$f}$r$p"
 
 	if [ $pcmode = yes ]; then
 		if [ "${__git_printf_supports_v-}" != yes ]; then

programming_language: Shell
filename: t9903-bash-prompt.sh
change_type: ModificationType.MODIFY
diff: @@ -452,53 +452,53 @@ test_expect_success 'prompt - format string starting with dash' '
 '
 
 test_expect_success 'prompt - pc mode' '
-	printf "BEFORE: (master):AFTER" >expected &&
+	printf "BEFORE: (\${__git_ps1_branch_name}):AFTER\\nmaster" >expected &&
 	printf "" >expected_output &&
 	(
 		__git_ps1 "BEFORE:" ":AFTER" >"$actual" &&
 		test_cmp expected_output "$actual" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - branch name' '
-	printf "BEFORE: (${c_green}master${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear}):AFTER\\nmaster" >expected &&
 	(
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" >"$actual"
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - detached head' '
-	printf "BEFORE: (${c_red}(%s...)${c_clear}):AFTER" $(git log -1 --format="%h" b1^) >expected &&
+	printf "BEFORE: (${c_red}\${__git_ps1_branch_name}${c_clear}):AFTER\\n(%s...)" $(git log -1 --format="%h" b1^) >expected &&
 	git checkout b1^ &&
 	test_when_finished "git checkout master" &&
 	(
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - dirty status indicator - dirty worktree' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_red}*${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_red}*${c_clear}):AFTER\\nmaster" >expected &&
 	echo "dirty" >file &&
 	test_when_finished "git reset --hard" &&
 	(
 		GIT_PS1_SHOWDIRTYSTATE=y &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - dirty status indicator - dirty index' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_green}+${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_green}+${c_clear}):AFTER\\nmaster" >expected &&
 	echo "dirty" >file &&
 	test_when_finished "git reset --hard" &&
 	git add -u &&
@@ -506,13 +506,13 @@ test_expect_success 'prompt - bash color pc mode - dirty status indicator - dirt
 		GIT_PS1_SHOWDIRTYSTATE=y &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - dirty status indicator - dirty index and worktree' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_red}*${c_green}+${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_red}*${c_green}+${c_clear}):AFTER\\nmaster" >expected &&
 	echo "dirty index" >file &&
 	test_when_finished "git reset --hard" &&
 	git add -u &&
@@ -521,25 +521,25 @@ test_expect_success 'prompt - bash color pc mode - dirty status indicator - dirt
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		GIT_PS1_SHOWDIRTYSTATE=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - dirty status indicator - before root commit' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_green}#${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_green}#${c_clear}):AFTER\\nmaster" >expected &&
 	(
 		GIT_PS1_SHOWDIRTYSTATE=y &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		cd otherrepo &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - inside .git directory' '
-	printf "BEFORE: (${c_green}GIT_DIR!${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear}):AFTER\\nGIT_DIR!" >expected &&
 	echo "dirty" >file &&
 	test_when_finished "git reset --hard" &&
 	(
@@ -547,13 +547,13 @@ test_expect_success 'prompt - bash color pc mode - inside .git directory' '
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		cd .git &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - stash status indicator' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_lblue}\$${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_lblue}\$${c_clear}):AFTER\\nmaster" >expected &&
 	echo 2 >file &&
 	git stash &&
 	test_when_finished "git stash drop" &&
@@ -561,29 +561,29 @@ test_expect_success 'prompt - bash color pc mode - stash status indicator' '
 		GIT_PS1_SHOWSTASHSTATE=y &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - bash color pc mode - untracked files status indicator' '
-	printf "BEFORE: (${c_green}master${c_clear} ${c_red}%%${c_clear}):AFTER" >expected &&
+	printf "BEFORE: (${c_green}\${__git_ps1_branch_name}${c_clear} ${c_red}%%${c_clear}):AFTER\\nmaster" >expected &&
 	(
 		GIT_PS1_SHOWUNTRACKEDFILES=y &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" &&
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '
 
 test_expect_success 'prompt - zsh color pc mode' '
-	printf "BEFORE: (%%F{green}master%%f):AFTER" >expected &&
+	printf "BEFORE: (%%F{green}\${__git_ps1_branch_name}%%f):AFTER\\nmaster" >expected &&
 	(
 		ZSH_VERSION=5.0.0 &&
 		GIT_PS1_SHOWCOLORHINTS=y &&
 		__git_ps1 "BEFORE:" ":AFTER" >"$actual"
-		printf "%s" "$PS1" >"$actual"
+		printf "%s\\n%s" "$PS1" "${__git_ps1_branch_name}" >"$actual"
 	) &&
 	test_cmp expected "$actual"
 '

programming_language: Shell