CVE-2026-73567: sm-crypto: Predictable SM2 key generation in Node.js: default RNG uses Math.random + wall clock

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes sm-crypto (npm) < 0.5.0, fixed in 0.5.0. Check your lockfile, including transitive dependencies.

What it is

sm-crypto provides JavaScript implementations of the Chinese cryptographic algorithms SM2, SM3, and SM4. Prior to 0.5.0, the default no-argument sm2.generateKeyPairHex() path in Node.js uses the module-wide SecureRandom instance in src/sm2/utils.js, supplied by jsbn@1.1.0, which seeds an ARC4 stream from Math.random() and new Date().getTime() because window.crypto.getRandomValues is unavailable even though globalThis.crypto exists. An attacker who can observe the process's Math.random() outputs and estimate the key-generation time can reconstruct the seed, recover generated SM2 private keys, and predict signing ephemeral scalars used to forge signatures. This issue is fixed in version 0.5.0.

From the GitHub advisory

Summary

sm-crypto (npm package 0.4.0, the latest release, published 2026-01-20) generates SM2 private keys and signing ephemeral scalars from a single module-wide RNG instance (src/sm2/utils.js: const rng = new SecureRandom()). SecureRandom is jsbn's PRNG, which seeds an ARC4 stream from window.crypto.getRandomValues when available. In Node.js — sm-crypto's primary runtime — window is undefined, so the CSPRNG branch is skipped and the seed pool is instead filled from Math.random() (V8 xorshift128+, recoverable from a few outputs) plus new Date().getTime() (wall clock, attacker-estimable).

Node does expose Web Crypto as globalThis.crypto, but jsbn checks window.crypto, not globalThis.crypto, so the secure path is never taken. Consequently every SM2 private key produced by the default sm2.generateKeyPairHex() and every signing ephemeral scalar is derived from non-cryptographic sources and is predictable by an attacker who can observe a few Math.random() outputs and estimate the generation time.

This is the library's default (no-argument) path; no caller-selected parameter or configuration is required to trigger it. It is reproduced end-to-end against the unmodified real npm packages (sm-crypto@0.4.0 + jsbn@1.1.0); the PoC below runs against the real installed package, not a copy. The defect is still present on the latest published version (0.4.0) and is not covered by any existing JuneAndGreen/sm-crypto issue (0 afldl issues exist; the most recent issues are unrelated SM3/HKDF/PBKDF2 feature requests).

Details

Weakness type: CWE-338.

Product: sm-crypto (npm) · Assigned by: GitHub_M · Published: 2026-08-13

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.44% probability of exploitation activity in the next 30 days; percentile 37.

Timeline

• 2026-07-24 — GitHub-reviewed advisory GHSA-vh45-f885-3848 published (critical)
• 2026-08-13 — CVE record published by GitHub_M
• 2026-08-14 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-vh45-f885-3848 github.com
2. CVE.org record CVE-2026-73567 cve.org
3. NVD entry CVE-2026-73567 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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