The flaw lies in the open‑type decoding routines of the asn1c compiler. Before version 1.2.5 the code performs a conditional null check on a member pointer but then unconditionally dereferences that pointer to calculate an offset. When the pointer is not initialized, the decoder performs null‑pointer arithmetic and a subsequent memory read, triggering a segmentation fault. This fault results in a crash of any program that uses the generated ASN.1 definitions, effectively denying service to that component.

The vulnerability affects the open‑source ASN.1 compiler released by mouse07410. Any build of asn1c earlier than release 1.2.5 is susceptible. Systems that link against modules compiled with these earlier versions, or that parse ASN.1 data containing open types—such as E2AP, which uses APER encoding—are directly impacted. Upstream references note that BER and OER encodings are also affected.

No EPSS score and no KEV entry are available, so the probability of exploitation is unknown. The attack surface requires an attacker to supply crafted ASN.1 data that exercises the open‑type decode path, which the affected code handles in a deterministic and local manner. Although the flaw does not allow arbitrary code execution or data disclosure, the resulting crash can interrupt critical services, posing a moderate operational risk.