# CVE-2018-18531: Use of Insufficiently Random Values in penggle:kaptcha

> Remote attackers can bypass CAPTCHA protections in the Kaptcha library by brute-forcing values generated with a weak random number generator.

- **Severity:** Critical 9.8 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Oct 2018
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-8q89-pwhh-7wfq

## What is CVE-2018-18531?

CVE-2018-18531 is a critical vulnerability in n/a, published on 19 Oct 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

text/impl/DefaultTextCreator.java, text/impl/ChineseTextProducer.java, and text/impl/FiveLetterFirstNameTextCreator.java in kaptcha 2.3.2 use the Random (rather than SecureRandom) function for generating CAPTCHA values, which makes it easier for remote attackers to bypass intended access restrictions via a brute-force approach.

Weakness: CWE-330 (Use of Insufficiently Random Values)

## Which versions are affected by CVE-2018-18531?

2 open source packages ship an affected version, including com.github.penggle:kaptcha. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `com.github.penggle:kaptcha` | Maven | All versions to 2.3.2 | None |
| `com.github.penggle:kaptcha` | Maven | All versions to 2.3.2 | None |

Products: Kaptcha Project Kaptcha.

## How do I fix CVE-2018-18531?

No fix has been published for CVE-2018-18531 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-18531 being exploited?

There is no known exploitation of CVE-2018-18531 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-18531 and fix it if it is affected.

What it is: CVE-2018-18531 is a critical vulnerability in n/a, published on 19 Oct 2018. 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-2018-18531 in the wild and no public exploit code.

Affected packages and fixed versions:
- com.github.penggle:kaptcha (Maven): affected all versions up to 2.3.2; no fix listed
- com.github.penggle:kaptcha (Maven): affected all versions up to 2.3.2; 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-2018-18531/ (Markdown: https://insights.sbomify.com/CVE-2018-18531/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-18531
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-18531
- OSV: https://osv.dev/vulnerability/CVE-2018-18531

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-18531/
Summaries are generated and may contain mistakes; the official description above is the record.