The NASA’s Interplanetary Overlay Network (ION) is an implementation of Delay/Disruption Tolerant Networking (DTN). A BPv7 bundle with a malformed extension block causes uncontrolled memory allocation inside ION-DTN 4.1.3s, leading to receiver thread termination and a Denial-of-Service (DoS). The triggering bundle contains an extension block starting at 0x85070201005bbb0e20b4ea001a000927c0.... The first byte in the extension block (0x85) indicates a CBOR array of five elements of which the first four are numbers (0x07, 0x02, 0x01, 0x00) but the fifth element is a byte string of length 27 (0x5bbb0e20b4ea001a000927c0...). The vulnerability seems to be due to processing the fifth element of the array (i.e., the byte string) as replacing it with a number makes the vulnerability no longer be triggered. While parsing this extension block, ION obtains a very large block length, which in the code in bei.c:764) seems to be passed from blockLength which is an unsigned int, to a 32 bit signed integer blkSize. The unsigned to signed conversion causes blkSize to hold the value of -369092043, which is then converted into a 64-bit unsigned value inside MTAKE(blkSize), resulting in an attempt to allocate an unrealistic amount of memory, causing the error. As of time of publication, no known patched versions of BPv7 exist.