CVE-2021-32489: 
NixOS vulnerability analysis and mitigation

An issue was discovered in the sendsecuremsg() function of Yubico yubihsm-shell through 2.0.3. The function does not correctly validate the embedded length field of an authenticated message received from the device because responsemsg.st.len=8 can be accepted but triggers an integer overflow, which causes CRYPTOcbc128decrypt (in OpenSSL) to encounter an undersized buffer and experience a segmentation fault. The yubihsm-shell project is included in the YubiHSM 2 SDK product (NVD).

The vulnerability occurs in the message parsing logic where messages with responsemsg.st.len = 8 are accepted. The session ID is read from the lowest memory position while the MAC is read from the highest memory position, allowing the fields to overlap. When both checks pass, the uint16t outlen variable is decremented too far by the combination of outlen -= 8 and out_len -= 1, causing it to overflow to 65535. This leads to OpenSSL being instructed to work on a buffer of size 65535 while the actual buffer is much smaller, resulting in a segmentation fault (Security Blog).

The vulnerability can lead to a denial of service through segmentation faults when processing malicious messages from a compromised HSM device. The issue affects applications using the yubihsm-shell component for HSM communication (NVD).

The vulnerability has been patched in YubiHSM 2 SDK version 2021.03 and libyubihsm version 2.1.0. Users should upgrade to these or later versions to mitigate the issue (Security Blog).