sjcl: Improper Verification of Cryptographic Signature
CVE-2026-4258 is a high-severity improper verification of cryptographic signature vulnerability in sjcl, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 1.0.9 as the first without the flaw, so updating sjcl to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update sjcl to 1.0.9 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Sjcl | sjcl | before 1.0.9 | 1.0.9 |
| Org.webjars.npm:sjcl | org.webjars.npm:sjcl | all versions | Not stated |
| Bitwiseshiftleft | Stanford Javascript Crypto Library | 1.0.8 and earlier | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by CNA (snyk.io).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.7 | High | CNA (snyk.io) |
| CVSS 3.1 | 7.5 | High | CNA (snyk.io) |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Verification of Cryptographic Signature
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
More Improper Verification of Cryptographic Signature vulnerabilities (CWE-347)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- gist.github.com/Kr0emer/2560f98edb10b0b34f2438cd63913c47Exploit, Mitigation, Third Party Advisory
- github.com/bitwiseshiftleft/sjcl/commit/ee307459972442a17beebc29dc331fffd8aff796
Technical write-ups (may include proof of concept)
- security.snyk.io/vuln/SNYK-JS-SJCL-15369617Exploit, Third Party Advisory
Other references
Recent Improper Verification of Cryptographic Signature vulnerabilities
- 9.0 Critical severity
- 9.1 Critical severity
- 8.8 High severity
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
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