[FFmpeg-devel] [PR] libavformat/http: reject HTTP header lines exceeding buffer size (PR #21392)

[rcx86 via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21392 opened by rcx86
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21392
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21392.patch

Overly long HTTP header lines were silently truncated. A malicious
server could exploit this to cause parsing issues or other unexpected
behavior.


>From a58623aef1677fdab028010325cfbb247c78d648 Mon Sep 17 00:00:00 2001
From: HACKE-RC <60568652+HACKE-RC@users.noreply.github.com>
Date: Mon, 29 Dec 2025 22:19:59 +0530
Subject: [PATCH] libavformat/http: reject HTTP header lines exceeding buffer
 size

Overly long HTTP header lines were silently truncated. A malicious
server could exploit this to cause parsing issues or other unexpected
behavior.
---
 libavformat/http.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/libavformat/http.c b/libavformat/http.c
index bd25a45636..422b1ecec5 100644
--- a/libavformat/http.c
+++ b/libavformat/http.c
@@ -827,6 +827,7 @@ static int http_get_line(HTTPContext *s, char *line, int line_size)
 {
     int ch;
     char *q;
+    int too_long = 0;
 
     q = line;
     for (;;) {
@@ -839,10 +840,20 @@ static int http_get_line(HTTPContext *s, char *line, int line_size)
                 q--;
             *q = '\0';
 
+            if (too_long) {
+                av_log(s, AV_LOG_ERROR,
+                       "HTTP header line exceeds buffer size (%d); rejecting\n",
+                       line_size);
+                return AVERROR_INVALIDDATA;
+            }
+
             return 0;
         } else {
-            if ((q - line) < line_size - 1)
+            if ((q - line) < line_size - 1) {
                 *q++ = ch;
+            } else {
+                too_long = 1;
+            }
         }
     }
 }
@@ -1659,7 +1670,8 @@ static int http_buf_read(URLContext *h, uint8_t *buf, int size)
                     s->chunksize);
 
             if (!s->chunksize && s->multiple_requests) {
-                http_get_line(s, line, sizeof(line)); // read empty chunk
+                if ((err = http_get_line(s, line, sizeof(line))) < 0)
+                    return err;
                 s->chunkend = 1;
                 return 0;
             }
-- 
2.49.1

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