CVE-2026-61810: libspdm: SPDM (DSP0274) FINISH transcript under-specifies the new 1.4 OpaqueData fields

libspdm is a sample implementation that follows the DMTF SPDM specifications. In version 1.4.0, both the FINISH request (Table 80) and the FINISHRSP response (Table 81) gained two new fields, OpaqueDataLength and OpaqueData, placed before the trailing signed/authenticated field. The transcript definitions used to compute and verify the FINISH signature, the FINISH HMAC (RequesterVerifyData), and the FINISHRSP HMAC (ResponderVerifyData) were not updated and still terminate with a step of the form. Per DSP0274, the "SPDM Header Fields" are only the four header bytes (SPDMVersion, RequestResponseCode, Param1, Param2). A literal reading therefore excludes OpaqueDataLength and OpaqueData, even though those fields are transmitted before the trailing signature/HMAC field. Because the signature/HMAC must cover every field transmitted before it to "protect the entire handshake against manipulation by an active attacker," an active attacker could otherwise modify the opaque data in flight without invalidating the signature or HMAC. This issue has been patched in version 1.4.1.