# CVE-2026-55840: Scoold: Open Redirect in getBackToUrl() allows phishing via domain-prefix startsWith bypass

> Attackers can redirect users to malicious sites after login via flawed URL validation, enabling phishing and credential theft in Scoold.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/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:** 15 Oct 2026
- **Updated:** 15 Oct 2026
- **Also known as:** GHSA-85fm-6f2v-74pq

## What is CVE-2026-55840?

CVE-2026-55840 is a medium-severity vulnerability in Erudika scoold, published on 15 Oct 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

Scoold is a Q&A and a knowledge sharing platform for teams. Prior to 1.69.1, the getBackToUrl() method in src/main/java/com/erudika/scoold/utils/HttpUtils.java validates the backto and returnto parameters with Strings.CI.startsWith against the configured server URL. An attacker can supply an absolute URL whose hostname begins with the legitimate hostname, causing URI.resolve() to retain the attacker URL and the prefix check to accept it. A victim who follows the crafted sign-in link can be redirected to an attacker-controlled domain after authentication, enabling phishing and possible credential or token theft. This issue is fixed in version 1.69.1.

Weakness: CWE-601 (URL Redirection to Untrusted Site)

## Which versions are affected by CVE-2026-55840?


## How do I fix CVE-2026-55840?

No fix has been published for CVE-2026-55840 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-55840 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55840 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55840 and fix it if it is affected.

What it is: CVE-2026-55840 is a medium-severity vulnerability in Erudika scoold, published on 15 Oct 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55840 exists.

Affected product: Erudika scoold. 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-2026-55840/ (Markdown: https://insights.sbomify.com/CVE-2026-55840/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55840
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55840
- OSV: https://osv.dev/vulnerability/CVE-2026-55840

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-55840/
Summaries are generated and may contain mistakes; the official description above is the record.