CVE-2020-35965 (published 2021-01-04T02:15Z)

decode_frame in libavcodec/exr.c in FFmpeg 4.3.1 has an out-of-bounds write because of errors in calculations of when to perform memset zero operations.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-787
cwe_name: Out-of-bounds Write
description: The product writes data past the end, or before the beginning, of the intended buffer.
extended_description: 
            
            
             
			 
         
         

Fix information:
repo_url: https://github.com/FFmpeg/FFmpeg
commit_details: repo_url: https://github.com/FFmpeg/FFmpeg
author: Michael Niedermayer
author_date: 2020-10-24 22:21:48+02:00
msg: avcodec/exr: Check ymin vs. h

Fixes: out of array access
Fixes: 26532/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-5613925708857344
Fixes: 27443/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-5631239813595136

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
repository: repo_url: https://github.com/FFmpeg/FFmpeg
repo_name: FFmpeg/FFmpeg
description: Mirror of https://git.ffmpeg.org/ffmpeg.git
repo_language: C
owner: FFmpeg
file_changes: filename: exr.c
change_type: ModificationType.MODIFY
diff: @@ -1830,7 +1830,7 @@ static int decode_frame(AVCodecContext *avctx, void *data,
     // Zero out the start if ymin is not 0
     for (i = 0; i < planes; i++) {
         ptr = picture->data[i];
-        for (y = 0; y < s->ymin; y++) {
+        for (y = 0; y < FFMIN(s->ymin, s->h); y++) {
             memset(ptr, 0, out_line_size);
             ptr += picture->linesize[i];
         }

programming_language: C
repo_url: https://github.com/FFmpeg/FFmpeg
commit_details: repo_url: https://github.com/FFmpeg/FFmpeg
author: Michael Niedermayer
author_date: 2020-10-25 00:23:12+02:00
msg: avcodec/exr: skip bottom clearing loop when its outside the image

Fixes: signed integer overflow: 1633771809 * 32960 cannot be represented in type 'int'
Fixes: 26532/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EXR_fuzzer-5613925708857344

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
repository: repo_url: https://github.com/FFmpeg/FFmpeg
repo_name: FFmpeg/FFmpeg
description: Mirror of https://git.ffmpeg.org/ffmpeg.git
repo_language: C
owner: FFmpeg
file_changes: filename: exr.c
change_type: ModificationType.MODIFY
diff: @@ -1842,13 +1842,14 @@ static int decode_frame(AVCodecContext *avctx, void *data,
 
     ymax = FFMAX(0, s->ymax + 1);
     // Zero out the end if ymax+1 is not h
-    for (i = 0; i < planes; i++) {
-        ptr = picture->data[i] + (ymax * picture->linesize[i]);
-        for (y = ymax; y < avctx->height; y++) {
-            memset(ptr, 0, out_line_size);
-            ptr += picture->linesize[i];
+    if (ymax < avctx->height)
+        for (i = 0; i < planes; i++) {
+            ptr = picture->data[i] + (ymax * picture->linesize[i]);
+            for (y = ymax; y < avctx->height; y++) {
+                memset(ptr, 0, out_line_size);
+                ptr += picture->linesize[i];
+            }
         }
-    }
 
     picture->pict_type = AV_PICTURE_TYPE_I;
     *got_frame = 1;

programming_language: C