A flaw was found in SSSD. The rsa_pub_key_to_ssh() function in src/util/cert/libcrypto/cert.c converts the RSA modulus and public exponent from an X.509 certificate into fixed-size stack buffers using BN_bn2bin(), without checking BN_num_bytes() against the destination sizes. The exponent buffer is 8 bytes and the modulus buffer is 2048 bytes in the reviewed configuration. RSA components exceeding those sizes can overwrite stack memory, causing the SSH responder to crash and potentially corrupting process state. The LDAP userCertificate;binary to SSH authorized-key lookup path requires an attacker-influenced certificate and ssh_use_certificate_keys=true. Certificate validation must succeed unless verification is explicitly disabled. The maintainer confirmed the 64-bit exponent buffer limit, the absence of prior SSSD key-size validation, and the feasibility of dynamic allocation; they consider this CVE-worthy because appropriately issued valid certificates may reach the conversion. No end-to-end arbitrary-code-execution exploit is established. Source report: PSIRTSUPT-25890, finding H-06.