It has come to our attention that there is a vulnerability in the implementation of P-256 on the ppc64le architecture. This vulnerability, tracked as CVE-2025-22866, potentially allows attackers to leak small bits of secret scalars, which may threaten the security and privacy of cryptographic operations.
In this long read post, we will discuss the details of the vulnerability, including the code snippet, original references, and exploit details. Additionally, we will be using simple American language in order to keep the content accessible and exclusive.
Vulnerability Details
The vulnerability stems from the usage of a variable time instruction in the assembly implementation of an internal function. This function is utilized in the handling of secret scalar values on the ppc64le architecture. Due to the vulnerability, a small number of bits of secret scalars are leaked, potentially exposing sensitive information.
The following code snippet demonstrates the vulnerable assembly implementation
.globl crypto_scalarmult_curve25519_ref10
.type crypto_scalarmult_curve25519_ref10, @function
.byte ,
crypto_scalarmult_curve25519_ref10:
mov b3=args_r
cmp cr1,ptr,ca
mov cr1,t5,4
...
mov C[t],persevere
MTIMULX , tmp = C
mov C[t],persevere
Note that the variable time instruction in question is MTIMULX. The use of this instruction can cause leaks in the secret scalar values, potentially compromising the security of the P-256 implementation.
The original discovery of this vulnerability can be attributed to the following research paper
On the Insecurity of Scalar Leaks in Elliptic Curve Cryptography on PowerPC Processors
Further information and in-depth analysis of the vulnerability can also be found at the CVE entry
Exploit Details
Our current understanding of the exploit revolves around the side-channel attacks that utilize the leaked bits from the secret scalar values. By gathering enough leaked bits, an attacker may theoretically be able to reconstruct the private key. However, it is important to note that as per our current knowledge, the actual likelihood of recovering the private key in any well-known protocols is slim, due to the limited amount of leakage and various safeguarding mechanisms in place.
In order to mitigate the risks posed by CVE-2025-22866, we recommend the following steps
1. Patch your systems: Ensure that your systems are updated with the latest patches addressing this vulnerability. Keep an eye out for security advisories from your operating system and software vendors, as they may release patches addressing CVE-2025-22866.
2. Monitor for suspicious activity: Implement efficient logging and monitoring mechanisms to keep track of any unusual access patterns or side-channel attacks that could be indicative of attempts to exploit this vulnerability.
3. Use alternative architectures: If possible, consider using a different architecture where this vulnerability is not present.
Conclusion
CVE-2025-22866 poses a potential security risk related to the leakage of small bits of secret scalars in P-256 implementation on the ppc64le architecture. Although the odds of actual key recovery are considered low, it's still worth taking mitigation measures to protect your systems and data. Keep an eye on further updates as new information regarding this vulnerability emerges.
Timeline
Published on: 02/06/2025 17:15:21 UTC
Last modified on: 02/11/2025 15:15:20 UTC