CVE-2023-26556

Vulnerability

Description CVE-2023-26556 is a timing side-channel vulnerability in io.finnet tss-lib before version 2.0.0. The root cause is the use of Go's crypto/elliptic library for scalar multiplication, which is not implemented in constant time due to an if statement inside a loop [1][2]. This non-constant-time implementation allows an attacker to observe timing variations during key generation, specifically in the ecdsa/keygen/round_2.go file [2].

Exploitation

An attacker who can precisely measure the time taken by the key generation process can exploit this side-channel to recover the secret key. The attack does not require network access to the signing operations, as the leakage occurs during key generation itself. No authentication is needed if the attacker can observe the timing remotely (e.g., via network latency analysis) or locally [2].

Impact

Successful exploitation leads to the complete disclosure of the secret key, compromising the threshold signature scheme. This means an attacker can produce valid signatures on behalf of the group or recover the private key. The vulnerability also affects forks like bnb-chain/tss-lib and thorchain/tss [2].

Mitigation

The fix is available in tss-lib version 2.0.0 and later. Users are strongly advised to upgrade immediately. The vulnerability is also tracked as GO-2023-1732 in the Go vulnerability database [4].