pretalx mail templates vulnerable to email injection via unescaped user-controlled placeholders

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-41426: 0.15% estimated exploitation activity in the next 30 days; percentile 4.58 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

An unauthenticated attacker can send arbitrary HTML-rendered emails from a pretalx instance's configured sender address by embedding malformed HTML or markdown link syntax in a user-controlled template placeholder such as the account display name. The most direct vector is the password-reset flow: the attacker registers an account with a malicious name, enters the victim's email address, and triggers a password reset. The resulting email is delivered from the event's legitimate sender address and passes SPF/DKIM/DMARC validation, making it a ready-made phishing vector. The same class of bug affects every mail template that interpolates a user-controlled placeholder (speaker name, proposal title, biography, question answers, etc.), including organiser-triggered emails such as acceptance/rejection notifications. Credits Thanks go to Mark Fijneman for finding and reporting a subset of this issue, which alerted us to the wider vulnerability.

Published by the source

18 Apr 2026, 01:11 UTC

Last modified by the source

8 Jun 2026, 19:15 UTC

Source last checked

26 Oct 2026, 13:44 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jm8c-9f3j-4378

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jm8c-9f3j-4378

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# Patch Next advisory brief: CVE-2026-41426

Advisory: pretalx mail templates vulnerable to email injection via unescaped user-controlled placeholders
IDs: CVE-2026-41426, GHSA-jm8c-9f3j-4378
Record: https://patchnext.com/advisories/cve-2026-41426 (revision 2, source checked 26 Oct 2026, 13:44 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pretalx 2026.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pretalx: affected < 2026.1.0; fixed in 2026.1.0

## Suggested inspection (read-only)
- `python -m pip show pretalx`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pretalx.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-jm8c-9f3j-4378 (OSV record GHSA-jm8c-9f3j-4378 lists affected ranges: PyPI pretalx >=0 <2026.1.0 (fixed))
- Verified: https://github.com/advisories/GHSA-jm8c-9f3j-4378 (GitHub-reviewed advisory GHSA-jm8c-9f3j-4378 lists affected ranges: PyPI pretalx >=0 <2026.1.0)

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