# CVE-2026-71981: Cypht < 2.12.2 PHP Object Injection RCE via back_query Parameter

> Authenticated attackers can achieve remote code execution by injecting a crafted PHP object into the back_query parameter of the logout handler.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Sep 2026
- **Updated:** 2 Sep 2026
- **Also known as:** GHSA-46j6-w3hw-4r9x

## What is CVE-2026-71981?

CVE-2026-71981 is a high-severity unsafe deserialization vulnerability in cypht-org cypht, published on 1 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Cypht before 2.12.2 contains a PHP object injection vulnerability that allows authenticated attackers to execute arbitrary operating system commands by supplying a crafted PHP object graph in the back_query GET parameter of the logout handler. Attackers can pass a base64-encoded serialized payload through this parameter, which is decoded and passed directly to unserialize() without an allow-list, signature check, or type restriction, enabling gadget-chain exploitation to achieve remote code execution as the web server process.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-71981?


## How do I fix CVE-2026-71981?

No fix has been published for CVE-2026-71981 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-71981 being exploited?

There is no known exploitation of CVE-2026-71981 in the wild and no public exploit code.

Public exploit code:

- Cypht CVE-2026-71981 PoC (github_poc): https://github.com/lyn4r/CVE-2026-71981

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71981 and fix it if it is affected.

What it is: CVE-2026-71981 is a high-severity unsafe deserialization vulnerability in cypht-org cypht, published on 1 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-71981 in the wild and no public exploit code.

Affected product: cypht-org cypht. 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-2026-71981/ (Markdown: https://insights.sbomify.com/CVE-2026-71981/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71981
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71981
- OSV: https://osv.dev/vulnerability/CVE-2026-71981

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-71981/
Summaries are generated and may contain mistakes; the official description above is the record.