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A flaw was found in SSSD. The sss_nss_protocol_parse_addr() function in the NSS responder (src/responder/nss/nss_protocol.c) extracts a 32-bit addrlen value from the client request but only validates that the body is at least 8 bytes, without checking that addrlen fits within the remaining packet body. This unvalidated length is passed through to talloc_memdup() in cache_req_data_create(), which copies addrlen bytes from the small request buffer, causing a heap-buffer-overflow read. A local attacker can trigger this by connecting to the world-writable NSS responder socket (/var/lib/sss/pipes/nss) and sending a SSS_NSS_GETHOSTBYADDR (0x0053) request with a large addrlen value and a valid address family payload so that inet_ntop() succeeds. Successful exploitation crashes the sssd_nss responder, causing a denial of service for NSS name resolution. Reported via PSIRTSUPT-20553 by BreachX Zero Day Labs.