An issue was discovered in the /api/connector endpoint handler in Yubico yubihsm-connector before 3.0.1 (in YubiHSM SDK before 2021.04). The handler did not validate the length of the request, which can lead to a state where yubihsm-connector becomes stuck in a loop waiting for the YubiHSM to send it data, preventing any further operations until the yubihsm-connector is restarted. An attacker can send 0, 1, or 2 bytes to trigger this.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-28484
• Yubico/yubihsm-connector@82bdf20
• https://github.com/Yubico/yubihsm-connector/releases
• https://www.yubico.com/support/security-advisories/ysa-2021-02/