# CVE-2026-12740: Plack::Middleware::OAuth versions through 0.10 for Perl do not support the OAuth 2.0 state parameter

> Attackers can link their provider account to a victim's session via CSRF, potentially gaining unauthorized access to the victim's account.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** No
- **Published:** 4 Jul 2026
- **Updated:** 6 Jul 2026
- **Also known as:** GHSA-rfx5-x6rx-6w25

## What is CVE-2026-12740?

CVE-2026-12740 is a high-severity vulnerability in CORNELIUS Plack::Middleware::OAuth, published on 4 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Plack::Middleware::OAuth versions through 0.10 for Perl do not support the OAuth 2.0 state parameter.

RequestTokenV2 builds the provider authorization redirect without issuing a state value, and AccessTokenV2 exchanges the callback code and registers the resulting token into the session (register_session) without verifying that the callback corresponds to an authorization request this session initiated.

Any application that uses this middleware for OAuth 2.0 login is exposed to login cross-site request forgery: because the callback is not bound to the session that began the flow, an attacker who starts an authorization with their own provider account can deliver the resulting callback to a victim, causing the victim's session to complete the attacker's authorization and associating the attacker's provider identity and access token with that session. Where the application persists this as an account link, the attacker may retain access to the victim's account through their own provider credentials.

Weakness: CWE-352 (Cross-Site Request Forgery)

## Which versions are affected by CVE-2026-12740?


## How do I fix CVE-2026-12740?

No fix has been published for CVE-2026-12740 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-12740 being exploited?

There is no known exploitation of CVE-2026-12740 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12740 and fix it if it is affected.

What it is: CVE-2026-12740 is a high-severity vulnerability in CORNELIUS Plack::Middleware::OAuth, published on 4 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-12740 in the wild and no public exploit code.

Affected product: CORNELIUS Plack::Middleware::OAuth. 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-2026-12740/ (Markdown: https://insights.sbomify.com/CVE-2026-12740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12740
- OSV: https://osv.dev/vulnerability/CVE-2026-12740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12740/
Summaries are generated and may contain mistakes; the official description above is the record.