# CVE-2026-89086: Security feature bypass in jose

> Attackers can bypass RSA signature validation in the OCaml jose library by exploiting incomplete PKCS #1 decoding checks.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Sep 2026
- **Updated:** 10 Sep 2026
- **Also known as:** GHSA-9r5j-37q2-cffw, OSEC-2026-19

## What is CVE-2026-89086?

CVE-2026-89086 is a critical vulnerability in OCaml jose, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the jose package before 0.11.0 for OCaml, library calls to validate an RSA signature only confirm that PKCS #1 decoding succeeds, and proceed to declare the signature valid without the required steps that involve the public key.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-89086?


## How do I fix CVE-2026-89086?

Upgrade to a fixed version.

## Is CVE-2026-89086 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89086 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89086 and fix it if it is affected.

What it is: CVE-2026-89086 is a critical vulnerability in OCaml jose, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89086 exists.

Affected product: OCaml jose. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89086/ (Markdown: https://insights.sbomify.com/CVE-2026-89086/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89086
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89086
- OSV: https://osv.dev/vulnerability/CVE-2026-89086

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-89086/
Summaries are generated and may contain mistakes; the official description above is the record.