[FFmpeg-devel] [PATCH 3/3] avformat/hls: Be more picky on extensions

[Michael Niedermayer]

This blocks disallowed extensions from probing
It also requires segments to have matching extensions to the format

It is recommended to set the whitelists correctly
instead of depending on extensions, but this should help a bit,
and this is easier to backport

Fixes: CVE-2023-6602 II. HLS Force TTY Demuxer
Fixes: CVE-2023-6602 IV. HLS XBIN Demuxer DoS Amplification

The other parts of CVE-2023-6602 have been fixed by prior commits

Found-by: Harvey Phillips of Amazon Element55 (element55)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavformat/hls.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/libavformat/hls.c b/libavformat/hls.c
index 045741c3b4e..a802eafc3fe 100644
--- a/libavformat/hls.c
+++ b/libavformat/hls.c
@@ -223,6 +223,7 @@ typedef struct HLSContext {
     AVDictionary *avio_opts;
     AVDictionary *seg_format_opts;
     char *allowed_extensions;
+    int extension_picky;
     int max_reload;
     int http_persistent;
     int http_multiple;
@@ -2114,6 +2115,24 @@ static int hls_read_header(AVFormatContext *s)
             pls->ctx->interrupt_callback = s->interrupt_callback;
             url = av_strdup(pls->segments[0]->url);
             ret = av_probe_input_buffer(&pls->pb.pub, &in_fmt, url, NULL, 0, 0);
+            if (c->extension_picky && ret >= 0) {
+                for (int n = 0; n < pls->n_segments; n++) {
+                    struct segment *seg = pls->segments[n];
+                    if ( strcmp(c->allowed_extensions, "ALL") &&
+                        !av_match_ext    (seg->url, c->allowed_extensions) &&
+                        !ff_match_url_ext(seg->url, c->allowed_extensions)) {
+                        av_log(s, AV_LOG_ERROR, "URL %s is not in allowed_extensions\n", seg->url);
+                        ret = AVERROR_INVALIDDATA;
+                    }
+
+                    if (!in_fmt->extensions ||
+                        !av_match_ext(    seg->url, in_fmt->extensions) &&
+                        !ff_match_url_ext(seg->url, in_fmt->extensions)) {
+                        av_log(s, AV_LOG_ERROR, "detected format extension %s mismatches url %s\n", in_fmt->extensions ? in_fmt->extensions : "none", seg->url);
+                        ret = AVERROR_INVALIDDATA;
+                    }
+                }
+            }
             if (ret < 0) {
                 /* Free the ctx - it isn't initialized properly at this point,
                 * so avformat_close_input shouldn't be called. If
@@ -2576,6 +2595,8 @@ static const AVOption hls_options[] = {
         OFFSET(allowed_extensions), AV_OPT_TYPE_STRING,
         {.str = "3gp,aac,avi,ac3,eac3,flac,mkv,m3u8,m4a,m4s,m4v,mpg,mov,mp2,mp3,mp4,mpeg,mpegts,ogg,ogv,oga,ts,vob,wav"},
         INT_MIN, INT_MAX, FLAGS},
+    {"extension_picky", "Be picky with all extensions matching",
+        OFFSET(extension_picky), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, FLAGS},
     {"max_reload", "Maximum number of times a insufficient list is attempted to be reloaded",
         OFFSET(max_reload), AV_OPT_TYPE_INT, {.i64 = 3}, 0, INT_MAX, FLAGS},
     {"m3u8_hold_counters", "The maximum number of times to load m3u8 when it refreshes without new segments",
-- 
2.48.1