Thomas Vegas discovered a heap-based buffer overflow in the function tftp_receive_packet() that receives data from a TFTP server. It can call recvfrom() with the default size for the buffer rather than with the size that was used to allocate it. Thus, the content that might overwrite the heap memory is controlled by the server. This issue was introduced by the add of the TFTP BLKSIZE option handling. It was previously incompletely fixed by an almost identical issue called CVE-2019-5436.
For Debian 7 Wheezy, these problems have been fixed in version 7.26.0-1+wheezy25+deb7u5.
We recommend that you upgrade your curl packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/