Linux Server Security Review
A build review with an attacker sitting at the keyboard: what the box exposes, what a low privileged user can reach, and how quickly that becomes root. CREST-certified testers, fixed price from £1,620, scoped in 24 hours.
- Unlimited retesting
- No rescheduling or cancellation fees
- Fixed quote within 24 hours
“I would highly recommend EJN Labs to any organisation seeking reliable, detailed, and well-managed penetration testing services, particularly for government or enterprise-level projects.”
Imran SaghirProject Lead, SquareOne“There wasn’t another company we could find that could deliver what we needed in the timeframe we needed. The client loved it, and we got instant ROI from the engagement.”
Dan WilcocksonCo-Founder, CelloriGold images drift. A package gets installed for a deployment and stays, a service is enabled for a migration and never disabled, a sudo rule is added for an engineer who left two years ago. The review starts from what is running today rather than what the standard says.
Hardening guides describe the build. We test the one you actually run.
The second question is escalation. Given a normal user account, which is what an application compromise provides, we go through the usual paths: sudo rules, writable service units, cron jobs, SUID binaries, container membership and kernel exposure.
Third, the neighbourhood. Keys that unlock other hosts, mounted shares, agent forwarding and credentials in configuration files are what turn one server into the rest of the estate.
ISO 27001, SOC 2, PCI DSS and Cyber Essentials Plus audits accept manual penetration test evidence. Scan-only evidence is generally insufficient.
LINUX SPECIFICS
What We Actually Test on a Linux Server
Ten areas that apply to a Linux build, on top of the standard infrastructure checks. Every finding is verified, reproducible and mapped to CIS benchmarks, CWE and CVSS 3.1.
Patch and support posture
Distribution and kernel versions, support status, and the exposure that follows from what is unpatched.
Accounts and authentication
Local accounts, shared logins, password and key policy, and account lifecycle.
Sudo and privilege rules
Sudo configuration, wildcards, scripts run as root, and what each rule really allows.
Local privilege escalation
SUID and capability review, writable service units, cron and timer jobs, and group membership such as docker.
SSH configuration
Authentication methods, key management, agent forwarding, and what a stolen key would unlock.
Service exposure
Listening services, their binding, and which of them are needed for the role the server performs.
File permissions and secrets
World readable configuration, credentials in files and history, and permissions on application directories.
Hardening controls
Firewall rules, mandatory access control, kernel parameters and the controls a benchmark expects.
Lateral movement
Trust between hosts, mounted shares, credentials reachable from this server and where they lead.
Logging and detection
Log configuration, retention, forwarding, and whether the activity in this review would be visible.
METHODOLOGY
What a Linux build finding looks like
Written the way a finding appears in our reports. The example below is reconstructed from publicly documented research, with hosts, paths and identifiers redacted. We do not republish client findings, named or anonymised.
Unpatched sudo gives any local user root on most of the estate
- Affected
- A build server at [redacted] reached with a low privileged service account, running a sudo package two years behind.
- What we found
- From an account with no sudo rules at all we triggered the heap overflow in argument parsing and obtained a root shell. The same package version was present on [redacted] of the hosts in scope.
- Why it matters
- Any user or compromised service on the host becomes root, including the continuous integration account, which held deployment keys for production.
- Fix
- Patch sudo across the estate, bring unattended upgrades into the build rather than adding them afterwards, and separate build runners so one host compromise does not carry production deployment keys.
Reconstructed from public research: CVE-2021-3156, known as Baron Samedit, a heap based buffer overflow in sudo, CVSS 3.1 base score 7.8.
Linux Server Penetration Testing: From Scope to Attestation
CREST-aligned methodology built on OWASP Web Security Testing Guide, OWASP ASVS, NIST SP 800-115, and PTES. Each finding maps to all four standards plus your specific compliance regime.
Reconnaissance
Application mapping, technology fingerprinting, content discovery, parameter enumeration, authentication-flow analysis, role-matrix construction.
Vulnerability Assessment
Authenticated and unauthenticated automated scanning across every user role, plus targeted manual checks for known weakness patterns.
Manual Exploitation
Hands-on testing by a CREST-certified pentester. Business-logic exploitation, chained vulnerabilities, privilege escalation, impact validation.
Reporting + Retest
Executive summary, technical report with CVSS scores and reproduction steps, walkthrough call, free retest after remediation, attestation letter.
CREDENTIALS
Verified Accreditations Auditors Accept
Every credential below is independently verifiable. UK procurement teams, FCA supervisors, ISO 27001 / SOC 2 auditors, and cyber insurance underwriters all recognise these standards.
GET YOUR QUOTE
Get a CREST Linux Server assessment pen test quote in 24 hours
A fixed-price quote back in one business day, from a named CREST assessor. No sales pipeline, no chasing.
- CREST and IASME accredited. Testing your auditors and clients already recognise.
- Fast-track testing within 24 hours where required. Free retest of every fix included.
- Live findings via your client portal, not a four-week PDF.
- Fixed price from £1,620 for a small, single-scope engagement, agreed up front. Most engagements run £2,580 and up. No day-rate surprises.
Dan WilcocksonCo-Founder, CelloriUnder NDA Further named references available on a scoping call.
- We reply within one business day with a fixed-price quote from a named CREST assessor.
- You approve the scope and we book a start date, usually within 24 hours.
- Live findings land in your client portal as we test, with a free retest of every fix.
Get your fixed pen test quote in 24 hours
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COMPLIANCE READY
Reports Mapped to Every Framework
Findings are explicitly tagged to the relevant control reference. Your audit team submits the report directly without translation work.
ISO 27001:2022
Annex A.8.8 management of technical vulnerabilities plus A.5.15-5.18 and A.8.2-8.5 access control validation.
SOC 2 Type I & II
CC6 logical access, CC7 system operations, CC8 change management evidence.
PCI DSS
Requirement 11.4 application penetration testing across cardholder data environments, including ecommerce penetration testing for online retail platforms.
FCA SYSC
SYSC 4.1.1R, 6.1.1R, 13 mapped to each finding for FCA-regulated firms.
UK GDPR
Article 32 effectiveness testing, customer-data security controls, ICO-acceptable evidence.
Cyber Essentials Plus
Direct certification through our IASME body status, single-vendor delivery.
PRICING
Transparent Linux Server Penetration Testing Pricing
Pricing depends on the number of builds and roles in scope, how much the estate varies from host to host, and the depth of the configuration review. The day count flexes; the included deliverables stay the same across all engagements.
1 to 2 days
Single user role, basic CRUD application, marketing website with auth. Typically 5-day engagement.
Get a fixed quote2 to 4 days
Multi-role SaaS, business application with payment integration. Typically 8-12 day engagement.
Get a fixed quote4 to 6 days
Multi-tenant platform, complex authorisation matrix, integration-heavy applications. 15-20 day engagement.
Get a fixed quotePart of Technologies We Pen Test. These are examples of the stacks we publish pages for, not a complete list. If yours is not here we still test it. Related pages:
BY SECTOR
Linux Server Penetration Testing for Your Sector
Sector-specialist scoping for UK businesses with sector-specific compliance regimes and threat models.
Fintech & FCA-Regulated
FCA SYSC, Open Banking FAPI 1.0, PSD2 SCA, payment-flow scrutiny, KYC/AML testing.
Fintech sector pageSaaS Companies
SOC 2 Type I & II evidence, multi-tenant boundaries, role escalation, customer-tenant isolation.
SaaS sector pageLaw Firms
SRA Cyber Standard, privileged data, conveyancing fraud defence, partner-tier procurement.
Law firm sector pageHealthcare
NHS DTAC, DSP Toolkit v6, UK GDPR Article 32, EHR systems, telehealth platforms.
Healthcare sector pageInsurance
FCA / PRA Operational Resilience, cyber underwriting, claims data, broker portals.
Insurance sector pagePublic Sector
CCS / G-Cloud framework, NCSC-aligned, citizen-facing services, PSN-compliance scrutiny.
Public sector pageWHY EJN LABS
What You Get From Linux Server Penetration Testing
Six concrete differentiators competitors don’t all match.
CREST-Certified Testers, Verifiable
Every test by a CREST-certified pen tester (CRT, CCT APP, CCT INF where applicable). Verify our company status at crest-approved.org.
24-Hour Startup, Where Required
From signed scope to active testing in a single business day for incident response, audit deadlines, or regulator-driven timelines.
Live Findings, Not 4-Week PDFs
Critical issues reported during testing through your client portal. Your team remediates while testing continues.
Audit-Ready Reports
Executive summary plus full technical report with CVSS scores and explicit framework mappings (ISO 27001, SOC 2, PCI DSS, FCA SYSC).
Free Retests, Standard
Verify remediation of every finding before close-out. Letter of attestation for audit submission included. Most competitors charge £1,500-£3,000 per retest.
UK-Based CREST Testers
Every engagement performed by vetted, UK-based CREST-certified testers, matched to your needs, security clearance, and compliance scope.
FAQ
Frequently Asked
Do you need root access?
No. We prefer to start as a normal user, because that is what an attacker gets. Root access makes the configuration review faster.
How many servers can you cover?
A small scope is one or two builds, standard a handful, enterprise a fleet with several roles. Sampling is fine and we say how we sampled.
Is this the same as an internal network test?
No. The internal test attacks the network from an unknown position. This reviews one build in detail.
Do you cover containers on the host?
Container escape and daemon exposure are in scope. Cluster security is the Kubernetes page.
Which distributions?
Debian and Ubuntu, Red Hat and derivatives, SUSE and Amazon Linux. The review is the same shape across them.
Will anything change on the server?
Nothing persists. Escalation proof of concept is agreed in advance and cleaned up afterwards.
What is included in the price?
Scoping, testing, the executive summary, the technical report, a walkthrough call and free retests until the finding is closed. One scope, one number, no follow-up invoices.
How fast can you start?
Scope to active testing in 24 hours once the scope is agreed, subject to tester availability in your window.
Are your testers CREST certified?
Yes. EJN Labs is a CREST member company and testing is delivered by CREST-qualified testers. The membership is verifiable on the CREST marketplace.
20+ CREST-accredited testing services in one place
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Get your Linux builds reviewed
Tell us the distributions and the roles they serve. You will have a fixed scope and a number within 24 hours.
