Gentoo: 202107-14 Critical: pptpd Remote Buffer Overflow Advisory

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GENTOO LINUX SECURITY ANNOUNCEMENT 200304-08
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- From advisory:

"PPTP packet header contain 16bit length which specifies the full size of
the packet:

        bytes_this = read(clientFd, packet + bytes_ttl, 2 - bytes_ttl);
        // ...
        bytes_ttl += bytes_this;
        // ...
        length = htons(*(u_int16_t *) packet);
        if (length > PPTP_MAX_CTRL_PCKT_SIZE) {
          // abort
        }

Looks good so far, except:

        bytes_this = read(clientFd, packet + bytes_ttl, length - bytes_ttl);

If given length was 0 or 1, the "length - bytes_ttl" result is -1 or -2,
which means that it reads unlimited amount of data from client into
"packet", which is a buffer located in stack.

The exploitability only depends on if libc allo...
Read the Full Advisory