CVE-2017-1000083 (published 2017-09-05T06:29Z)

backend/comics/comics-document.c (aka the comic book backend) in GNOME Evince before 3.24.1 allows remote attackers to execute arbitrary commands via a .cbt file that is a TAR archive containing a filename beginning with a "--" command-line option substring, as demonstrated by a --checkpoint-action=exec=bash at the beginning of the filename.

Severity: MEDIUM
CVSS v2 base score: 6.8 (AV:N/AC:M/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 7.8, HIGH (CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: NVD-CWE-noinfo
cwe_name: Insufficient Information
description: There is insufficient information about the issue to classify it; details are unkown or unspecified.
extended_description: Insufficient Information

Fix information:
repo_url: https://github.com/GNOME/evince
commit_details: repo_url: https://github.com/GNOME/evince
author: Bastien Nocera
author_date: 2017-07-06 20:02:00+02:00
msg: comics: Remove support for tar and tar-like commands

When handling tar files, or using a command with tar-compatible syntax,
to open comic-book archives, both the archive name (the name of the
comics file) and the filename (the name of a page within the archive)
are quoted to not be interpreted by the shell.

But the filename is completely with the attacker's control and can start
with "--" which leads to tar interpreting it as a command line flag.

This can be exploited by creating a CBT file (a tar archive with the
.cbt suffix) with an embedded file named something like this:
"--checkpoint-action=exec=bash -c 'touch ~/hacked;'.jpg"

CBT files are infinitely rare (CBZ is usually used for DRM-free
commercial releases, CBR for those from more dubious provenance), so
removing support is the easiest way to avoid the bug triggering. All
this code was rewritten in the development release for GNOME 3.26 to not
shell out to any command, closing off this particular attack vector.

This also removes the ability to use libarchive's bsdtar-compatible
binary for CBZ (ZIP), CB7 (7zip), and CBR (RAR) formats. The first two
are already supported by unzip and 7zip respectively. libarchive's RAR
support is limited, so unrar is a requirement anyway.

Discovered by Felix Wilhelm from the Google Security Team.

https://bugzilla.gnome.org/show_bug.cgi?id=784630
repository: repo_url: https://github.com/GNOME/evince
repo_name: GNOME/evince
description: Read-only mirror of https://gitlab.gnome.org/GNOME/evince
repo_language: C
owner: GNOME
file_changes: filename: comics-document.c
change_type: ModificationType.MODIFY
diff: @@ -56,8 +56,7 @@ typedef enum
 	RARLABS,
 	GNAUNRAR,
 	UNZIP,
-	P7ZIP,
-	TAR
+	P7ZIP
 } ComicBookDecompressType;
 
 typedef struct _ComicsDocumentClass ComicsDocumentClass;
@@ -117,9 +116,6 @@ static const ComicBookDecompressCommand command_usage_def[] = {
 
         /* 7zip */
 	{NULL               , "%s l -- %s"     , "%s x -y %s -o%s", FALSE, OFFSET_7Z},
-
-        /* tar */
-	{"%s -xOf"          , "%s -tf %s"      , NULL             , FALSE, NO_OFFSET}
 };
 
 static GSList*    get_supported_image_extensions (void);
@@ -364,13 +360,6 @@ comics_check_decompress_command	(gchar          *mime_type,
 			comics_document->command_usage = GNAUNRAR;
 			return TRUE;
 		}
-		comics_document->selected_command =
-				g_find_program_in_path ("bsdtar");
-		if (comics_document->selected_command) {
-			comics_document->command_usage = TAR;
-			return TRUE;
-		}
-
 	} else if (g_content_type_is_a (mime_type, "application/x-cbz") ||
 		   g_content_type_is_a (mime_type, "application/zip")) {
 		/* InfoZIP's unzip program */
@@ -396,12 +385,6 @@ comics_check_decompress_command	(gchar          *mime_type,
 			comics_document->command_usage = P7ZIP;
 			return TRUE;
 		}
-		comics_document->selected_command =
-				g_find_program_in_path ("bsdtar");
-		if (comics_document->selected_command) {
-			comics_document->command_usage = TAR;
-			return TRUE;
-		}
 
 	} else if (g_content_type_is_a (mime_type, "application/x-cb7") ||
 		   g_content_type_is_a (mime_type, "application/x-7z-compressed")) {
@@ -425,27 +408,6 @@ comics_check_decompress_command	(gchar          *mime_type,
 			comics_document->command_usage = P7ZIP;
 			return TRUE;
 		}
-		comics_document->selected_command =
-				g_find_program_in_path ("bsdtar");
-		if (comics_document->selected_command) {
-			comics_document->command_usage = TAR;
-			return TRUE;
-		}
-	} else if (g_content_type_is_a (mime_type, "application/x-cbt") ||
-		   g_content_type_is_a (mime_type, "application/x-tar")) {
-		/* tar utility (Tape ARchive) */
-		comics_document->selected_command =
-				g_find_program_in_path ("tar");
-		if (comics_document->selected_command) {
-			comics_document->command_usage = TAR;
-			return TRUE;
-		}
-		comics_document->selected_command =
-				g_find_program_in_path ("bsdtar");
-		if (comics_document->selected_command) {
-			comics_document->command_usage = TAR;
-			return TRUE;
-		}
 	} else {
 		g_set_error (error,
 			     EV_DOCUMENT_ERROR,

programming_language: C
filename: configure.ac
change_type: ModificationType.MODIFY
diff: @@ -795,7 +795,7 @@ AC_SUBST(TIFF_MIME_TYPES)
 AC_SUBST(APPDATA_TIFF_MIME_TYPES)
 AM_SUBST_NOTMAKE(APPDATA_TIFF_MIME_TYPES)
 if test "x$enable_comics" = "xyes"; then
-        COMICS_MIME_TYPES="application/x-cbr;application/x-cbz;application/x-cb7;application/x-cbt;application/x-ext-cbr;application/x-ext-cbz;application/vnd.comicbook+zip;application/x-ext-cb7;application/x-ext-cbt"
+        COMICS_MIME_TYPES="application/x-cbr;application/x-cbz;application/x-cb7;application/x-ext-cbr;application/x-ext-cbz;application/vnd.comicbook+zip;application/x-ext-cb7;"
         APPDATA_COMICS_MIME_TYPES=$(echo "<mimetype>$COMICS_MIME_TYPES</mimetype>" | sed -e 's/;/<\/mimetype>\n    <mimetype>/g')
         if test -z "$EVINCE_MIME_TYPES"; then
            EVINCE_MIME_TYPES="${COMICS_MIME_TYPES}"

programming_language: Shell