The reported flaw is an integer underflow in the IPv6 extension-header parsing routine of Nmap. When a scanner processes a crafted IPv6 response that contains a truncated extension header, the parser calculates a remaining length that underflows, resulting in an out‑of‑bounds read before the program crashes. This vulnerability does not grant code execution or system compromise; at worst it causes the scanning tool to crash, denying its availability. The weakness corresponds to CWE‑191 (Integer Underflow or Wraparound).

The weakness is present in the Nmap network mapping tool from the Nmap project. Vulnerable releases include all Nmap versions 7.99 and earlier. No other vendors or product lines are impacted according to the available data.

The CVSS score for this issue is 6.9, indicating a moderate severity and a likelihood that an unauthenticated attacker can affect the stability of the scanning host. EPSS is not available, so the current probability of exploitation cannot be determined, and the flaw is not listed in the CISA KEV catalog. The attack vector is remote, requiring an attacker to send a specially crafted IPv6 packet to a host that is performing a raw IPv6 scan. If such a packet is processed, the scanner will crash, interrupting the scan and potentially impacting operations in environments that rely on continuous vulnerability assessment. No privilege escalation or confidentiality compromise is possible with this flaw.