# CVE-2025-65849: Altcha Proof-of-Work obfuscation mode cryptanalytic break

> Attackers can bypass Altcha Proof-of-Work obfuscation to recover nonces, defeating bot protection mechanisms in npm packages.

- **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:** No
- **Published:** 8 Dec 2025
- **Updated:** 11 Dec 2025
- **Also known as:** GHSA-mpmc-qchh-r9q8

## What is CVE-2025-65849?

CVE-2025-65849 is a critical vulnerability in n/a, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A cryptanalytic break in Altcha Proof-of-Work obfuscation mode version 0.8.0 and later allows for remote visitors to recover the Proof-of-Work nonce in constant time via mathematical deduction. NOTE: this is disputed by the Supplier because the product's objective is "to discourage automated scraping / bots, not guarantee resistance to determined attackers." The documentation states “the goal is not to provide a secure cryptographic algorithm but to use a proof-of-work mechanism that allows any capable device to decrypt the hidden data.”

Weakness: CWE-327 (Use of a Broken or Risky Cryptographic Algorithm)

## Which versions are affected by CVE-2025-65849?

2 open source packages ship an affected version, including altcha.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `altcha` | npm | From 0.8.0 to 2.2.4 | None |
| `altcha` | npm | From 0.8.0 to 2.2.4 | None |

## How do I fix CVE-2025-65849?

No fix has been published for CVE-2025-65849 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-65849 being exploited?

There is no known exploitation of CVE-2025-65849 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-65849 and fix it if it is affected.

What it is: CVE-2025-65849 is a critical vulnerability in n/a, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-65849 in the wild and no public exploit code.

Affected packages and fixed versions:
- altcha (npm): affected from 0.8.0 up to 2.2.4; no fix listed
- altcha (npm): affected from 0.8.0 up to 2.2.4; no fix listed

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-2025-65849/ (Markdown: https://insights.sbomify.com/CVE-2025-65849/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-65849
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-65849
- OSV: https://osv.dev/vulnerability/CVE-2025-65849

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-65849/
Summaries are generated and may contain mistakes; the official description above is the record.