In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: fix OOB read in decode_choice() In decode_choice(), the boundary check before get_len() uses the variable len, which is still 0 from its initialization at the top of the function: unsigned int type, ext, len = 0; ... if (ext || (son-attr & OPEN)) { BYTE_ALIGN(bs); if (nf_h323_error_boundary(bs, len, 0)) / len is 0 here / return H323_ERROR_BOUND; len = get_len(bs)

/ OOB read / When the bitstream is exactly consumed (bs-cur == bs-end), the check nf_h323_error_boundary(bs, 0, 0) evaluates to (bs-cur + 0 > bs-end), which is false. The subsequent get_len() call then dereferences *bs-cur++, reading 1 byte past the end of the buffer. If that byte has bit 7 set, get_len() reads a second byte as well. This can be triggered remotely by sending a crafted Q.931 SETUP message with a User-User Information Element containing exactly 2 bytes of PER-encoded data ({0x08, 0x00}) to port 1720 through a firewall with the nf_conntrack_h323 helper active. The decoder fully consumes the PER buffer before reaching this code path, resulting in a 1-2 byte heap-buffer-overflow read confirmed by AddressSanitizer. Fix this by checking for 2 bytes (the maximum that get_len() may read) instead of the uninitialized len. This matches the pattern used at every other get_len() call site in the same file, where the caller checks for 2 bytes of available data before calling get_len().