Opened 6 years ago

Closed 6 years ago

#5992 closed defect (fixed)

Heap-overflow in http.c results Remote Code Execution

Reported by: Paul Ch Owned by:
Priority: critical Component: avformat
Version: git-master Keywords: http crash SIGSEGV
Cc: Blocked By:
Blocking: Reproduced by developer: yes
Analyzed by developer: no

Description

Summary of the bug:

We managed to find and successfully exploit critical security bug in libavformat/http.c that results Remote Code Execution in latest version of FFmpeg.

Prerequisites:

Attacker has to reproduce SSRF bug and send HTTP request to his remote host. There are multiple ways of doing this already described all over the Internet. (For ex. you can trigger SSRF using HLS playlists or the way I described earlier in this ticket ).

Overview:

libavformat/http.c supports different types of HTTP responses, one of them is "Transfer-Encoding: chunked". Because int64_t type is used to store size of the chunk and strtoll function to parse the value of next chunk size it is possible to pass negative value and it will be successfully stored in chunksize variable. Later FFMIN function is used to determine final size of chunk and now it turns negative and it is passed to http_buf_read function. Inside http_buf_read function our negative value is assigned to len variable and passed as argument to memcpy which results a crash.

Steps to reproduce:

I am attaching PoC file that reproduces the simple crash. Steps to reproduce bug:

$ python http_poc.py &
$ ffmpeg -v trace -i "http://localhost:12345/1.avi" 1.avi
$ gdb -q ffmpeg_g 
(gdb) r -v trace -i "http://localhost:12345/1.avi" 1.avi

I am also attaching gdb stack-trace.

Recommended fix:

The best fix for that should be completely rewrite http parser, because some sneaky bugs still can be found there. Good example of http parser can be found here, it is implemented with finite-state machine.

But for now simple quick fix could be making chunksize unsigned long long.

Final words:

Our team is planning to release full exploit and blogpost with full details on exploitation in 30 days or as soon as you patch vulnerability.

Contact me if you need more details on vulnerability.

Attachments (2)

http_poc.py (575 bytes ) - added by Paul Ch 6 years ago.
PoC
http_gdb_output.txt (3.0 KB ) - added by Paul Ch 6 years ago.
gdb stack trace

Download all attachments as: .zip

Change History (8)

by Paul Ch, 6 years ago

Attachment: http_poc.py added

PoC

by Paul Ch, 6 years ago

Attachment: http_gdb_output.txt added

gdb stack trace

comment:1 by Paul Ch, 6 years ago

Summary: Heap-overflow results Remote Code ExecutionHeap-overflow in http.c results Remote Code Execution

comment:2 by James, 6 years ago

For future reference, please report vulnerabilities you find to ffmpeg-security@ffmpeg.org as mentioned in https://ffmpeg.org/security.html instead of posting them on this bug tracker.

in reply to:  description comment:3 by James, 6 years ago

Replying to paulch:

Contact me if you need more details on vulnerability.

Sending this information to the above email address nonetheless would also be appreciated.

in reply to:  description ; comment:4 by Carl Eugen Hoyos, 6 years ago

Keywords: http crash SIGSEGV added
Reproduced by developer: set
Status: newopen

Replying to paulch:

But for now simple quick fix could be making chunksize unsigned long long.

I believe all valid bug reports on this bug tracker are very much appreciated, no matter if security relevant or not but I don't understand why you didn't send a patch with this change to the development mailing list.

in reply to:  4 comment:5 by Paul Ch, 6 years ago

Thanks for your feedback. All future bug reports will be submitted to ffmpeg-security@ffmpeg.org .

Patches have been already proposed by FFmpeg developers and reviewed by our team.
Thank you.

comment:6 by Carl Eugen Hoyos, 6 years ago

Resolution: fixed
Status: openclosed
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