Open5GS EUVD-2026-109914

Exploitation requires a UDM instance explicitly configured with home-network (hnet) de-conceal private keys - without these keys the vulnerable parse_scheme_output() SUCI de-concealment path is not reached, which is the reason for the AC:H rating. Given that configuration, a remote unauthenticated UE or SBI peer must submit a crafted SUCI whose scheme-output hits the minimum accepted length (42 bytes) to the UDM. Limiting factors: the non-default de-conceal-key configuration, the high crafting precision (AT:P / AC:H), affected versions limited to Open5GS 2.6.1 through 2.8.0, and the fact that the over-read is only 3-4 bytes, read-only, silent under talloc, and never placed on the wire - so there is no attacker-observable disclosure and no crash in practice.

This is a genuinely low-priority issue despite the medium 6.3 CVSS 4.0 base score, and the signals are largely consistent on that point. The CVSS 4.0 vector (AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N) shows a network-reachable, unauthenticated flaw but with high attack complexity and a present attack requirement, and only low confidentiality impact with no integrity or availability impact. No EPSS score and no CISA KEV listing are provided in the input, and the GHSA advisory itself classifies this as a 'low-severity hardening issue, read-only and config-gated.' The vuln.today decision label is 'this_month' (routine patching), not act_now or emergency. Critically, the advisory states the over-read bytes are only 3-4 bytes past the allocation and are never placed on the wire and the operation is silent under talloc - so even the VC:L confidentiality rating overstates practical impact, because the attacker gains nothing observable. The one limiting factor that most reduces real-world exposure is that the code path is config-gated: it is only reachable when a UDM is configured with home-network (hnet) de-conceal private keys, which is why the advisory assigns AC:H. Net: a real, confirmed bug worth patching on a normal cycle, but not an urgent or high-impact threat.

On a 5G core where the UDM is configured with hnet home-network de-conceal private keys, a remote unauthenticated UE or SBI peer sends a crafted SUCI whose scheme-output is the minimum accepted 42-byte length to the UDM's SUCI de-concealment path. The incomplete length check in parse_scheme_output() (which omits OGS_MSIN_LEN) causes a heap over-read of 3-4 bytes past the allocated buffer during the MAC-tag memcpy. A private proof-of-concept exists (the reporter offers it on request and demonstrated the over-read under an ASan build); no public exploit code is available, and because the over-read bytes are not returned to the attacker, the scenario yields no data disclosure or crash in practice.