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

Severity: medium (CVSS 5.1 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-07 · updated 2026-06-17
Weakness: CWE-601

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.

Affected products

saltcorn: before 1.4.6; from 1.5.0-beta.0, < 1.5.6; from 1.6.0-alpha.0, < 1.6.0-beta.5

References

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