Insight: Misaligned Expectations—STIG Hardening for Amazon Linux 2023 and the RHEL Confusion
Insight: Misaligned Expectations—STIG Hardening for Amazon Linux 2023 and the RHEL Confusion
Note from the Field
If you're using EC2 Image Builder to STIG-harden Amazon Linux 2023, heads up—you're likely mapped against the wrong OS baseline. AL2023 is being treated like RHEL8, but it aligns more closely with RHEL9 or Fedora. That misalignment causes real issues: SELinux isn’t installed, some packages are missed, and the hardening script quietly skips critical steps. This isn’t a beginner’s problem—it’s one of those senior DevOps calls where you either override the mapping or rebuild the compliance path yourself. Here's what we’re seeing and why it matters.
The Problem Emerges in EC2 Image Builder
Security-focused AWS teams often rely on EC2 Image Builder with STIG hardening components to automate compliance. But something subtle—and significant—is going wrong when that pipeline is applied to Amazon Linux 2023 (AL2023). A recent discovery shows that AWS is currently treating AL2023 as if it shares compatibility with RHEL8, even though the structure and behavior of AL2023 align much more closely with RHEL9.
This mismatch quietly breaks hardening steps. SELinux is skipped. DNF-based packages are misidentified or excluded. Some security checks pass, but others are never run. As a result, the system appears hardened but isn't fully protected.
Clarifying the Technical Mismatch
Amazon Linux 2023 is a Fedora-derived distribution that uses dnf, includes modern kernel features, and expects newer policy packages. STIG mappings that assume RHEL8 (which uses older conventions, different package names, and sometimes yum) will fail in nuanced ways. You won’t always get an error—but you’ll end up with a security baseline that's incomplete.
For instance, if the STIG component attempts to configure SELinux using RHEL8-style logic, it may silently skip installation. That’s a glaring gap for any system expected to pass compliance or operate in a zero-trust environment.
Why It Matters
DevOps and cloud security engineers rely on automation to maintain velocity and enforce consistency. But automation is only as good as the assumptions behind it. When AWS-managed components misalign the OS with the wrong baseline, those assumptions fall apart—and you're left with a hardened-in-name-only system.
In compliance-heavy sectors (finance, government, healthcare), that’s not just an inconvenience—it’s a liability. Engineers may think their instances meet STIG requirements, but when a real audit hits, discrepancies will emerge. Worse, real-world exploits may succeed because assumed protections were never applied.
What You Can Do
For now, there is no official AWS advisory or GitHub issue documenting this behavior. That may change, but in the meantime, experienced teams can take matters into their own hands:
Some engineers are already working around the issue with custom components. If your team has already done this, consider sharing your findings in AWS Slack, on GitHub, or in a blog post to help others catch the issue early.
Final Thoughts
This is the kind of sharp edge that only shows up in senior-level infrastructure work. It’s not a documentation miss—it’s a subtle misalignment of assumptions at the heart of AWS’s automation tooling. If you rely on Image Builder for compliance, take a moment to confirm your mappings. One misstep in the baseline, and the whole pyramid of security starts to wobble.
The Problem Emerges in EC2 Image Builder
Security-focused AWS teams often rely on EC2 Image Builder with STIG hardening components to automate compliance. But something subtle—and significant—is going wrong when that pipeline is applied to Amazon Linux 2023 (AL2023). A recent discovery shows that AWS is currently treating AL2023 as if it shares compatibility with RHEL8, even though the structure and behavior of AL2023 align much more closely with RHEL9.
This mismatch quietly breaks hardening steps. SELinux is skipped. DNF-based packages are misidentified or excluded. Some security checks pass, but others are never run. As a result, the system appears hardened but isn't fully protected.
Clarifying the Technical Mismatch
Amazon Linux 2023 is a Fedora-derived distribution that uses dnf, includes modern kernel features, and expects newer policy packages. STIG mappings that assume RHEL8 (which uses older conventions, different package names, and sometimes yum) will fail in nuanced ways. You won’t always get an error—but you’ll end up with a security baseline that's incomplete.
For instance, if the STIG component attempts to configure SELinux using RHEL8-style logic, it may silently skip installation. That’s a glaring gap for any system expected to pass compliance or operate in a zero-trust environment.
Why It Matters
DevOps and cloud security engineers rely on automation to maintain velocity and enforce consistency. But automation is only as good as the assumptions behind it. When AWS-managed components misalign the OS with the wrong baseline, those assumptions fall apart—and you're left with a hardened-in-name-only system.
In compliance-heavy sectors (finance, government, healthcare), that’s not just an inconvenience—it’s a liability. Engineers may think their instances meet STIG requirements, but when a real audit hits, discrepancies will emerge. Worse, real-world exploits may succeed because assumed protections were never applied.
What You Can Do
For now, there is no official AWS advisory or GitHub issue documenting this behavior. That may change, but in the meantime, experienced teams can take matters into their own hands:
- Override the default STIG mapping in EC2 Image Builder to align with RHEL9 or a custom Fedora-based mapping.
- Explicitly install SELinux and verify policies in a post-build validation phase.
- Audit the hardening logs closely, especially if Image Builder reports success despite key packages missing from the image.
Some engineers are already working around the issue with custom components. If your team has already done this, consider sharing your findings in AWS Slack, on GitHub, or in a blog post to help others catch the issue early.
Final Thoughts
This is the kind of sharp edge that only shows up in senior-level infrastructure work. It’s not a documentation miss—it’s a subtle misalignment of assumptions at the heart of AWS’s automation tooling. If you rely on Image Builder for compliance, take a moment to confirm your mappings. One misstep in the baseline, and the whole pyramid of security starts to wobble.
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Written by Aaron Rose, software engineer and technology writer at Tech-Reader.blog.
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