Skip to content

Commit 189ff42

Browse files
committed
avformat/hls: Check local file extensions
This reduces the attack surface of local file-system information leaking. It prevents the existing exploit leading to an information leak. As well as similar hypothetical attacks. Leaks of information from files and symlinks ending in common multimedia extensions are still possible. But files with sensitive information like private keys and passwords generally do not use common multimedia filename extensions. It does not stop leaks via remote addresses in the LAN. The existing exploit depends on a specific decoder as well. It does appear though that the exploit should be possible with any decoder. The problem is that as long as sensitive information gets into the decoder, the output of the decoder becomes sensitive as well. The only obvious solution is to prevent access to sensitive information. Or to disable hls or possibly some of its feature. More complex solutions like checking the path to limit access to only subdirectories of the hls path may work as an alternative. But such solutions are fragile and tricky to implement portably and would not stop every possible attack nor would they work with all valid hls files. Developers have expressed their dislike / objected to disabling hls by default as well as disabling hls with local files. There also where objections against restricting remote url file extensions. This here is a less robust but also lower inconvenience solution. It can be applied stand alone or together with other solutions. limiting the check to local files was suggested by nevcairiel This recommits the security fix without the author name joke which was originally requested by Nicolas. Found-by: Emil Lerner and Pavel Cheremushkin Reported-by: Thierry Foucu <tfoucu@google.com> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
1 parent c0702ab commit 189ff42

File tree

1 file changed

+17
-1
lines changed

1 file changed

+17
-1
lines changed

Diff for: libavformat/hls.c

+17-1
Original file line numberDiff line numberDiff line change
@@ -204,6 +204,7 @@ typedef struct HLSContext {
204204
char *http_proxy; ///< holds the address of the HTTP proxy server
205205
AVDictionary *avio_opts;
206206
int strict_std_compliance;
207+
char *allowed_extensions;
207208
} HLSContext;
208209

209210
static int read_chomp_line(AVIOContext *s, char *buf, int maxlen)
@@ -618,8 +619,19 @@ static int open_url(AVFormatContext *s, AVIOContext **pb, const char *url,
618619
return AVERROR_INVALIDDATA;
619620

620621
// only http(s) & file are allowed
621-
if (!av_strstart(proto_name, "http", NULL) && !av_strstart(proto_name, "file", NULL))
622+
if (av_strstart(proto_name, "file", NULL)) {
623+
if (strcmp(c->allowed_extensions, "ALL") && !av_match_ext(url, c->allowed_extensions)) {
624+
av_log(s, AV_LOG_ERROR,
625+
"Filename extension of \'%s\' is not a common multimedia extension, blocked for security reasons.\n"
626+
"If you wish to override this adjust allowed_extensions, you can set it to \'ALL\' to allow all\n",
627+
url);
628+
return AVERROR_INVALIDDATA;
629+
}
630+
} else if (av_strstart(proto_name, "http", NULL)) {
631+
;
632+
} else
622633
return AVERROR_INVALIDDATA;
634+
623635
if (!strncmp(proto_name, url, strlen(proto_name)) && url[strlen(proto_name)] == ':')
624636
;
625637
else if (av_strstart(url, "crypto", NULL) && !strncmp(proto_name, url + 7, strlen(proto_name)) && url[7 + strlen(proto_name)] == ':')
@@ -2134,6 +2146,10 @@ static int hls_probe(AVProbeData *p)
21342146
static const AVOption hls_options[] = {
21352147
{"live_start_index", "segment index to start live streams at (negative values are from the end)",
21362148
OFFSET(live_start_index), AV_OPT_TYPE_INT, {.i64 = -3}, INT_MIN, INT_MAX, FLAGS},
2149+
{"allowed_extensions", "List of file extensions that hls is allowed to access",
2150+
OFFSET(allowed_extensions), AV_OPT_TYPE_STRING,
2151+
{.str = "3gp,aac,avi,flac,mkv,m3u8,m4a,m4s,m4v,mpg,mov,mp2,mp3,mp4,mpeg,mpegts,ogg,ogv,oga,ts,vob,wav"},
2152+
INT_MIN, INT_MAX, FLAGS},
21372153
{NULL}
21382154
};
21392155

0 commit comments

Comments
 (0)