# CVE-2026-42259: Saltcorn: Open Redirect in `POST /auth/login` due to incomplete `is_relative_url` validation (backslash bypass)

> Attackers can redirect users to malicious sites after login via a backslash bypass in the destination parameter, requiring user interaction.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA: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:** Yes
- **Published:** 7 May 2026
- **Updated:** 8 May 2026
- **Also known as:** GHSA-f3g8-9xv5-77gv

## What is CVE-2026-42259?

CVE-2026-42259 is a medium-severity vulnerability in saltcorn, published on 7 May 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

Saltcorn is an extensible, open source, no-code database application builder. Prior to versions 1.4.6, 1.5.6, and 1.6.0-beta.5, Saltcorn validates the post-login dest parameter with a string check that only blocks :/ and //. Because all WHATWG-compliant browsers normalise backslashes (\) to forward slashes (/) for special schemes, a payload such as /\evil.com/path slips through is_relative_url(), is emitted unchanged in the HTTP Location header, and causes the browser to navigate cross-origin to an attacker-controlled domain. The bug is reachable on a default install and only requires a victim who can be tricked into logging in via a crafted Saltcorn URL. This issue has been patched in versions 1.4.6, 1.5.6, and 1.6.0-beta.5.

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

## Which versions are affected by CVE-2026-42259?

6 open source packages ship an affected version, including @saltcorn/server.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@saltcorn/server` | npm | All versions | 1.4.6 |
| `@saltcorn/server` | npm | All versions | 1.4.6 |
| `@saltcorn/server` | npm | From 1.5.0-beta.0 | 1.5.6 |
| `@saltcorn/server` | npm | From 1.5.0-beta.0 | 1.5.6 |
| `@saltcorn/server` | npm | From 1.6.0-alpha.0 | 1.6.0-beta.5 |
| `@saltcorn/server` | npm | From 1.6.0-alpha.0 | 1.6.0-beta.5 |

## How do I fix CVE-2026-42259?

Upgrade @saltcorn/server to a fixed version for your release line: 1.4.6, 1.5.6 or 1.6.0-beta.5.

## Is CVE-2026-42259 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42259 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42259 and fix it if it is affected.

What it is: CVE-2026-42259 is a medium-severity vulnerability in saltcorn, published on 7 May 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-2026-42259 exists.

Affected packages and fixed versions:
- @saltcorn/server (npm): affected all versions; fixed in 1.4.6
- @saltcorn/server (npm): affected all versions; fixed in 1.4.6
- @saltcorn/server (npm): affected from 1.5.0-beta.0; fixed in 1.5.6
- @saltcorn/server (npm): affected from 1.5.0-beta.0; fixed in 1.5.6
- @saltcorn/server (npm): affected from 1.6.0-alpha.0; fixed in 1.6.0-beta.5
- @saltcorn/server (npm): affected from 1.6.0-alpha.0; fixed in 1.6.0-beta.5

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-2026-42259/ (Markdown: https://insights.sbomify.com/CVE-2026-42259/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42259
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42259
- OSV: https://osv.dev/vulnerability/CVE-2026-42259

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42259/
Summaries are generated and may contain mistakes; the official description above is the record.