# CVE-2026-49953: Discuz! X5.0 CAPTCHA Bypass via Predictable Character Set

> Attackers can bypass CAPTCHA protections in Discuz! X5.0 using OCR models, enabling automated abuse of login and registration features.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Jun 2026
- **Updated:** 28 Jul 2026
- **Also known as:** GHSA-p3qj-vw7q-v9pc

## What is CVE-2026-49953?

CVE-2026-49953 is a medium-severity vulnerability in Discuz! X5.0, published on 15 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Discuz! X5.0 releases 20260320 through 20260610 contains a CAPTCHA bypass vulnerability that allows unauthenticated remote attackers to defeat challenge controls by exploiting limited complexity and predictable character sets in generated CAPTCHA images. Attackers can train a custom optical character recognition model against collected CAPTCHA samples to reliably predict challenge text, bypassing protections on login, registration, and other functionality from automated abuse.

Weakness: CWE-804 (Guessable CAPTCHA)

## Which versions are affected by CVE-2026-49953?


## How do I fix CVE-2026-49953?

No fix has been published for CVE-2026-49953 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-49953 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49953 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49953 and fix it if it is affected.

What it is: CVE-2026-49953 is a medium-severity vulnerability in Discuz! X5.0, published on 15 Jun 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-2026-49953 exists.

Affected product: Discuz! X5.0. 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-2026-49953/ (Markdown: https://insights.sbomify.com/CVE-2026-49953/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49953
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49953
- OSV: https://osv.dev/vulnerability/CVE-2026-49953

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49953/
Summaries are generated and may contain mistakes; the official description above is the record.