MajorDoMo update‑poisoning RCE: a supply‑chain wake‑up call

MajorDoMo update poisoning allows unauthenticated RCE and webshell installs with two GET requests, a supply chain wake-up call for business

What happened, in plain words

About 58 minutes ago a critical vulnerability in MajorDoMo was disclosed that lets an unauthenticated attacker force the application to fetch a malicious update and drop files straight into the webroot. The flaw lives in an update mechanism that reads an attacker-controlled update URL, fetches an Atom feed with trivial validation, downloads a tarball with TLS verification disabled (CURLOPT_SSL_VERIFYPEER set to FALSE), runs a tar extract command, then copies files into the document root. According to the advisory, an attacker can deploy arbitrary PHP files including webshells with just two GET requests.

Since the exploit works without authentication it’s not theoretical. It’s immediate and noisy, and any exposed MajorDoMo instance that permits outbound update fetches could be at risk right now.

Why this matters to your business

Although MajorDoMo is the specific product at risk here, the lesson scales to any system that pulls code or updates from the internet. If updates can be poisoned, attackers can bypass nearly every perimeter you think you have. That means data theft, persistent backdoors, pivoting to other internal systems, and likely regulatory headaches if customer data is involved.

While the technical detail is interesting, the board will ask different questions. Can you prove who has access to systems, how updates are authorised, and that backups will restore business operations without reintroducing the compromise? If you can’t, expect downtime, forensic bills and awkward conversations with regulators or customers.

How this kind of flaw is exploited

Given the advisory’s sequence, the attack is supply-chain style. The update logic trusts an external feed, disables TLS checks, extracts code with shell commands, and writes to web directories. That’s a perfect chain for remote code execution. It’s the kind of failure where one misstep is all an attacker needs.

What attackers can do once they’re in

They can drop webshells to maintain access, quietly harvest credentials, modify site content, deploy ransomware, or create footholds for broader network intrusion. They can also hide by altering logs or overwriting backups, which makes recovery harder and more expensive.

What happens if you ignore this

Although you hope it won’t, ignoring supply-chain weaknesses gives attackers months of quiet access. Recovery costs spiral. Contracts get cancelled. Trust erodes. Leaders waste time on crisis calls. Meanwhile your teams are left investigating old logs and asking why the updates were allowed to run as root.

While backups are vital, they’re useless if they contain the compromised code you never detected. Untested backups are parachutes you have never bothered to open. Just saying.

How ISO 27001 and sensible controls would help

Although no standard is magic, an ISO 27001 information security management system encourages the exact controls that would reduce this risk: supplier and third-party risk assessment, change control, secure configuration management, least privilege for services that perform updates, and documented procedures around external feeds and code signing.

Since business continuity matters when a webroot is owned, an ISO 22301 business continuity plan helps you keep serving customers, paying staff and restoring services in a controlled way after an incident like this.

Following basic certification and hygiene will also help. For example, Cyber Essentials and IASME encourage practical measures such as patching, account management and boundary filtering that reduce the blast radius of a compromised web application.

Immediate actions you should take, right now

If you run MajorDoMo, or any system that auto-updates from the internet, do the following straight away:

• Isolate affected instances from the internet where possible, and block outbound update hosts at the network edge
• Audit update mechanisms, looking for external feed URLs, disabled TLS verification or commands that extract archives via shell
• Search for unexpected PHP files, webshell indicators, or recent file changes in the document root
• Preserve forensic images before doing wide restores, and change credentials where a compromise is suspected
• Test backups off‑site to ensure they’re not carrying the same compromise

Although the list above is immediate triage, longer term actions include enforcing code signing for updates, restricting the user context that performs updates, segmenting management interfaces from public networks and applying strict supplier security requirements in contracts.

How Synergos-style services fit, without the hard sell

Since this is a supplier and process problem as much as a coding mistake, you might consider a few practical steps: threat-led supplier assessments, an ISO 27001 aligned risk review of update processes, and security awareness training so teams know to question any strange update behaviour. Synergos’ pages on ISO 27001, ISO 22301, Cyber Essentials and IASME, and security awareness training show practical routes you can take to tighten supplier controls, improve change management and harden recovery plans.

Although this isn’t a ticket for fear, it is a ticket for action. Supplier and update hygiene are manageable, practical steps that stop simple attacks from becoming catastrophic ones.

A short, sensible plan for the next 48 hours

Start with discovery. Find every installation that can reach external update feeds. Patch or block them. Verify your backups off-host. Run a focused incident review if you find evidence of compromise. Then lock down update mechanisms and add cryptographic verification for future updates.

Although taking these steps won’t be fun, they will keep you out of the headlines, and that is worth bothering about.

Think of this as a reminder that trust in software updates must be earned, not assumed.