CVE-2026-22698: RustCrypto Elliptic Curves Disclosure Flaw

CVE-2026-22698 Overview

A critical Insecure Random Number Generation vulnerability has been identified in the RustCrypto Elliptic Curves library's SM2 Public Key Encryption (PKE) implementation. The vulnerability stems from a unit mismatch error in the ephemeral nonce generation function, which requests only 32 bits of randomness instead of the required 256 bits. This severe entropy reduction degrades the encryption security from a 128-bit level to a trivially attackable 16-bit level, enabling practical cryptographic attacks.

Critical Impact

Attackers can recover the ephemeral nonce k and decrypt any ciphertext using only the public key and ciphertext, completely compromising the confidentiality guarantees of SM2 PKE encryption.

Affected Products

• RustCrypto SM2 Crate version 0.14.0-pre.0
• RustCrypto SM2 Crate version 0.14.0-rc.0
• Applications using affected RustCrypto elliptic-curves library versions

Discovery Timeline

• 2026-01-10 - CVE-2026-22698 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2026-22698

Vulnerability Analysis

This vulnerability represents a fundamental cryptographic implementation error classified under CWE-331 (Insufficient Entropy). The SM2 Public Key Encryption scheme relies on the generation of an ephemeral random scalar k during the encryption process. This nonce must be generated with sufficient entropy to ensure that the encryption remains secure against brute-force and algebraic attacks.

In the affected versions, a unit mismatch error in the nonce generation code path causes the random number generator to be called with a parameter requesting 32 bits instead of 256 bits of randomness. The practical consequence is that the keyspace for the ephemeral nonce is reduced from 2^256 possible values to merely 2^32 values. Given modern computational capabilities, an attacker can exhaustively search this reduced keyspace in trivial time.

Once the attacker recovers the ephemeral nonce k, they can compute the shared secret and decrypt the ciphertext without access to the private key. This completely negates the security properties of the SM2 PKE scheme.

Root Cause

The root cause is a unit mismatch error in the nonce generation function within the SM2 PKE implementation. The function responsible for generating the ephemeral scalar k incorrectly specifies the entropy requirement in bits rather than bytes (or vice versa), resulting in only 32 bits of randomness being requested from the underlying random number generator instead of the cryptographically required 256 bits. This implementation bug effectively reduces the security parameter of the encryption from 128 bits to approximately 16 bits.

Attack Vector

The attack vector is network-based and requires no privileges, authentication, or user interaction. An attacker who intercepts SM2 PKE ciphertext encrypted with an affected library version can:

1. Observe the ephemeral public point in the ciphertext
2. Exhaustively search the 2^32 possible nonce values
3. For each candidate nonce, compute the corresponding ephemeral public point
4. When a match is found, use the recovered nonce to compute the shared secret
5. Decrypt the ciphertext to recover the plaintext

The attack is entirely passive and offline—once ciphertext is captured, the attacker can perform the decryption without any further interaction with the target system. Given that 2^32 operations is trivially achievable on commodity hardware, this attack is practical for any adversary with access to the ciphertext.

Detection Methods for CVE-2026-22698

Indicators of Compromise

• Presence of RustCrypto SM2 crate versions 0.14.0-pre.0 or 0.14.0-rc.0 in Cargo.lock files
• Applications compiled with affected elliptic-curves library versions performing SM2 encryption operations
• Dependency trees containing vulnerable pre-release SM2 implementations

Detection Strategies

• Perform software composition analysis (SCA) scans to identify RustCrypto SM2 crate versions in deployed applications
• Audit Cargo.toml and Cargo.lock files across Rust projects for affected version strings
• Implement CI/CD pipeline checks to flag pre-release cryptographic library dependencies
• Use cargo audit with updated advisory databases to automatically detect vulnerable dependencies

Monitoring Recommendations

• Monitor cryptographic library update advisories from the RustCrypto project via GitHub Security Advisories
• Subscribe to RustSec advisory notifications for the elliptic-curves crate family
• Implement continuous dependency monitoring for production Rust applications using SM2 cryptography
• Track commit references e4f7778 and 4781762 to verify patch application status

How to Mitigate CVE-2026-22698

Immediate Actions Required

• Immediately audit all Rust applications for usage of SM2 crate versions 0.14.0-pre.0 or 0.14.0-rc.0
• Update to a patched version of the SM2 crate containing commit e4f7778
• Re-encrypt any sensitive data that was previously encrypted using the vulnerable versions
• Consider any ciphertext generated with affected versions as potentially compromised

Patch Information

The RustCrypto maintainers have addressed this vulnerability in commit e4f7778. The fix corrects the unit mismatch error to ensure the full 256 bits of entropy are requested during ephemeral nonce generation. Developers should update their Cargo.toml to reference a version containing this fix and rebuild affected applications. Review the pull request #1600 for additional implementation details.

Workarounds

• Avoid using SM2 PKE functionality in affected pre-release versions until patched
• If immediate patching is not feasible, consider temporarily switching to an alternative elliptic curve implementation
• For applications that cannot be immediately updated, avoid processing new sensitive data with SM2 encryption
• Implement application-layer encryption using unaffected cryptographic primitives as an interim measure

# Update Cargo.toml to use patched version and rebuild
cargo update -p sm2
cargo audit
cargo build --release