javascript: Improper Check for Unusual or Exceptional Conditions
CVE-2026-42349 is a high-severity improper check for unusual or exceptional conditions vulnerability in javascript from Clerk, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected javascript versions: >= 5.22.0, < 5.125.10; >= 6.0.0, < 6.7.5. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.25% 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 Clerk/astro to 2.17.11 or 3.0.18, whichever matches your release line, or a later version.
- Update Clerk/backend to 2.33.3 or 3.2.14, whichever matches your release line, or a later version.
- Update Clerk/chrome-extension to 2.9.15 or 3.1.15, whichever matches your release line, or a later version.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Clerk | javascript | >= 5.22.0, < 5.125.10; >= 6.0.0, < 6.7.5 | Not stated |
| @clerk | shared | >= 3.0.0, <= 3.47.4; >= 4.0.0, <= 4.8.2 | Not stated |
| @clerk | backend | >= 2.0.0, <= 2.33.2; >= 3.0.0, <= 3.2.13 | Not stated |
| @clerk | nextjs | >= 6.0.0, <= 6.39.2; >= 7.0.0, <= 7.2.3 | Not stated |
| @clerk | clerk-react | >= 5.9.0, <= 5.61.5 | Not stated |
| @clerk | react | >= 6.0.0, <= 6.4.2 | Not stated |
| @clerk | vue | >= 1.0.0, <= 1.17.20; >= 2.0.0, <= 2.0.15 | Not stated |
| @clerk | astro | >= 2.0.0, <= 2.17.10; >= 3.0.0, <= 3.0.17 | Not stated |
| @clerk | nuxt | >= 1.0.0, <= 1.13.28; >= 2.0.0, <= 2.2.4 | Not stated |
| @clerk | clerk-expo | >= 2.2.11, <= 2.19.35 | Not stated |
| @clerk | expo | >= 3.0.0, <= 3.2.1 | Not stated |
| @clerk | react-router | >= 0.0.1, <= 2.4.12; >= 3.0.0, <= 3.1.3 | Not stated |
| @clerk | tanstack-react-start | >= 0.0.1, <= 0.29.10; >= 1.0.0, <= 1.1.3 | Not stated |
| @clerk | chrome-extension | >= 1.3.5, <= 2.9.14; >= 3.0.0, <= 3.1.14 | Not stated |
| @clerk | fastify | >= 1.0.42, <= 2.6.30; >= 3.0.0, <= 3.1.15 | Not stated |
| @clerk | express | >= 0.1.0, <= 1.7.78; >= 2.0.0, <= 2.1.5 | Not stated |
| @clerk | hono | >= 0.0.2, <= 0.1.15 | Not stated |
| Clerk | Clerk/astro | 2.0.0 up to, but not including, 2.17.11; 3.0.0 up to, but not including, 3.0.18 | 2.17.11, 3.0.18 |
| Clerk | Clerk/backend | 2.0.0 up to, but not including, 2.33.3; 3.0.0 up to, but not including, 3.2.14 | 2.33.3, 3.2.14 |
| Clerk | Clerk/chrome-extension | 1.3.5 up to, but not including, 2.9.15; 3.0.0 up to, but not including, 3.1.15 | 2.9.15, 3.1.15 |
| Clerk | Clerk/clerk-expo | 2.2.11 up to, but not including, 2.19.36 | 2.19.36 |
| Clerk | Clerk/clerk-js | 5.22.0 up to, but not including, 5.125.10; 6.0.0 up to, but not including, 6.7.5 | 5.125.10, 6.7.5 |
| Clerk | Clerk/clerk-react | 5.9.0 up to, but not including, 5.61.6 | 5.61.6 |
| Clerk | Clerk/express | 0.1.0 up to, but not including, 1.7.79; 2.0.0 up to, but not including, 2.1.6 | 1.7.79, 2.1.6 |
| Clerk | Clerk/fastify | 1.0.42 up to, but not including, 2.6.31; 3.0.0 up to, but not including, 3.1.16 | 2.6.31, 3.1.16 |
Version data comes from the organisation that assigned the CVE; 7 further products are omitted here. 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
- LowA basic user account is enough.
- 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
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.6 | High | CNA (github.com) |
| CVSS 3.1 | 8.1 | High | NVD |
Official description
Clerk JavaScript is the official JavaScript repository for Clerk authentication. has(), auth.protect(), and related authorization predicates in @clerk/shared, @clerk/nextjs, @clerk/backend, and other framework SDKs can return true for certain combined authorization checks when the result should be false, allowing a gated action to proceed for a user who does not satisfy the full set of requested conditions. This call shape can be bypassed if certain conditions are met: a has() or auth.protect() call that combines a reverification check with any of role, permission, feature, or plan, or that combines a billing check (feature or plan) with a role or permission check. This vulnerability is fixed in @clerk/clerk-js 5.125.10 and 6.7.5.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Check for Unusual or Exceptional Conditions
The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
How developers prevent this class of flaw
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Choose languages with features such as exception handling that force the programmer to anticipate unusual conditions that may generate exceptions. Custom exceptions may need to be developed to handle unusual business-logic conditions. Be careful not to pass sensitive exceptions back to the user (CWE-209, CWE-248).
- Check the results of all functions that return a value and verify that the value is expected.
- If using exception handling, catch and throw specific exceptions instead of overly-general exceptions (CWE-396, CWE-397). Catch and handle exceptions as locally as possible so that exceptions do not propagate too far up the call stack (CWE-705). Avoid unchecked or uncaught exceptions where feasible (CWE-248).
More Improper Check for Unusual or Exceptional Conditions vulnerabilities (CWE-754)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in javascript
- 7.4 High severity
- 7.5 High severity
- 9.8 Critical severity
Recent Improper Check for Unusual or Exceptional Conditions vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.9 High severity
- 7.8 High severity
- 9.8 Critical severity
- 8.7 High severity
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