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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- Proof of concept public, per CISA
- Fix
- Fixed in 2026-11
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Attacker must be a domain administrator of at least one domain, acting through their own authenticated session Triggered by one authenticated outbound message sent from that domain Affected mailcow-dockerized master commit and rspamd 4.2.1-1
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- First public exploit on GitHub Nov 10
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 40/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- 1 proof of concept on GitHub
- Exploitation: poc
- Automatable: no
- Technical impact: total
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.
Read the original 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.
cve.now Index
- Exploitation22/40Public exploit on Exploit-DB or GitHub
- Exposure8/25Specific setups only, reachable over the network
- Reach?/20Unknown. No tracked technology or package matched
- Severity10/10CVSS 9.4, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 68 if added to CISA KEV
- Would score about 63 if CISA's SSVC rates exploitation active
- Would score about 47 if CISA's SSVC rates it automatable
What to do
Check whether your setup matches what the bug needs.
Attacker must be a domain administrator of at least one domain, acting through their own authenticated session Triggered by one authenticated outbound message sent from that domain Affected mailcow-dockerized master commit and rspamd 4.2.1-1Upgrade to a fixed version: 2026-11.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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.
Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: no · Technical impact: total
- Record last updated
- Exploit code on GitHub
Faceless0x7/CVE-2026-125757
Affected versions
- mailcow mailcow: dockerized
fixed in 2026-11
Evidence 8
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Public exploit code · 1
Establishes: Public exploit code exists (Exploit-DB, Metasploit, Nuclei and GitHub).
- Exploit
Other links · 4
- Patch
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-125757
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: cve.now feed data
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: github.com
Which versions are affected by CVE-2026-125757?
mailcow: dockerized: before 2026-11.Source: cve.now feed data
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: github.com
How do I fix CVE-2026-125757?
Upgrade mailcow: dockerized to 2026-11 or later.Source: github.com