Microsoft has confirmed that Azure Linux images contain a vulnerable version of the Apache HTTP Server, alerting customers to a software regression that can expose raw source code to attackers. The advisory, posted by the Microsoft Security Response Center (MSRC) for CVE-2024-39884, places Azure Linux officially in scope—but it stops short of ruling out other Microsoft products that may also ship the flawed component.

The Bug: When Legacy Configurations Turn Dangerous

CVE-2024-39884 is a regression introduced in Apache HTTP Server 2.4.60, released in early July 2024. Under specific—but common—configurations, Apache can fail to apply the correct handler to a requested file and instead deliver its raw contents directly to the browser. For example, if a server uses legacy AddType directives to map .php files to the PHP interpreter, an attacker who crafts an indirect request (such as through an Alias or RewriteRule) might receive the PHP source code as plaintext rather than its executed output.

This flaw is not a remote code execution vulnerability, but source code disclosure can be equally damaging in real-world deployments. Configuration files, database credentials, API keys, and proprietary business logic all live inside server-side scripts. Leaking them can give attackers the blueprint they need to escalate an intrusion.

Apache documented the regression and shipped a partial fix in version 2.4.61, released on August 14, 2024. That fix addressed the core handler dispatch logic but missed an edge case, which was subsequently resolved in version 2.4.62 on September 11, 2024. The Apache Software Foundation’s changelog and several downstream advisories now consider 2.4.62 the definitive remediation point.

Microsoft’s Advisory: What It Reveals, and What It Doesn’t

On its Security Update Guide for CVE-2024-39884, MSRC states that Azure Linux “includes this open-source library and is therefore potentially affected by this vulnerability.” The entry links to a blog post explaining Microsoft’s new practice of publishing CSAF (Common Security Advisory Framework) and VEX (Vulnerability Exploitability eXchange) attestations, which began rolling out in October 2025.

Crucially, the MSRC entry also says: “If impact to additional products is identified, we will update the CVE to reflect this.” This wording is intentional. It means that, as of today, Azure Linux is the only Microsoft product for which the company makes an affirmative statement of possible impact. It does not mean that Azure Linux is the only product that actually contains the vulnerable Apache build.

In practice, Microsoft’s software estate is vast and includes many artifacts that bundle or rely on Apache HTTP Server: Azure Marketplace virtual machine images (both first- and third-party), App Service runtime containers, Azure Container Registry base images, GitHub Actions runner images, Windows Subsystem for Linux distributions, and internal tooling. The absence of an MSRC attestation for those items is not evidence of safety—it is simply a reflection of the phased rollout of Microsoft’s vulnerability disclosure program.

What This Means for You, Depending on Your Role

For Azure Linux Administrators

If you run Azure Linux images provided by Microsoft, you are directly affected. Treat this vulnerability as confirmed and move immediately to remediation. Microsoft’s package repositories for Azure Linux should contain patched versions that align with Apache 2.4.62; update via the standard package manager (tdnf update apache or equivalent). Verify the installed version with httpd -v and ensure you are at 2.4.62 or later.

For Cloud Architects and Security Teams Outside Azure Linux

You cannot rely solely on the MSRC advisory to clear your environment. Any Microsoft-supplied or third-party image that ships an Apache HTTP Server binary must be independently checked. This includes:

  • Azure Marketplace appliances and partner VM images
  • App Service built-in runtime stacks (for PHP, Python, etc.) that embed Apache
  • Container images pulled from Microsoft Container Registry
  • GitHub-hosted and self-hosted Actions runner images used in CI/CD
  • WSL instances and developer workstations

Run package manager commands (rpm -q httpd or dpkg -l apache2) inside these environments or use container scanning tools (Trivy, Clair, Anchore) to detect versions. For third-party Marketplace images, demand an SBOM (Software Bill of Materials) or a VEX attestation from the publisher, and perform your own scans in a staging environment before deploying.

For Developers and Web Hosting Providers

If you manage Apache configurations directly, immediately audit your handler mappings. Legacy AddType/AddHandler directives are the primary trigger for this regression. Replace them with explicit SetHandler or <FilesMatch> blocks that unambiguously assign a handler only to files in designated directories. For example:

<FilesMatch \.php$>
    SetHandler application/x-httpd-php
</FilesMatch>

This change not only mitigates CVE-2024-39884 but also follows current best practices for web server configuration. Additionally, review all Alias, ScriptAlias, and RewriteRule directives to ensure they do not inadvertently map into directories containing source code that should remain inaccessible.

How We Got Here: A Timeline of a Regression

The story begins with Apache HTTP Server 2.4.60, released on July 1, 2024, which introduced a change to the core request-handling code. While the exact code path is complex, the regression caused legacy content-type-based handler mappings to be ignored for requests that are not direct file hits—typically those routed through Alias or complex mod_rewrite rules. The Apache developers classified this as a high-severity issue because of the potential for source code disclosure.

  • July 1, 2024: Apache 2.4.60 released, unknowingly containing the regression.
  • August 5, 2024: CVE-2024-39884 reserved and initially disclosed by security researchers.
  • August 14, 2024: Apache releases 2.4.61 with a partial fix. The advisory acknowledges the vulnerability but notes that the fix was incomplete for certain configurations.
  • September 4, 2024: Follow-up issue CVE-2024-40725 is assigned to the incomplete fix, as the original handler miss still occurred in specific indirect request scenarios.
  • September 11, 2024: Apache releases 2.4.62, which incorporates the full fix and is considered the definitive remediation.
  • October 2025: Microsoft begins publishing CSAF/VEX attestations, including for Azure Linux images, which brings the advisory to the attention of a new set of customers.

The gap between the upstream fix and Microsoft’s public attestation highlights the reality of large-scale software supply chains: vulnerabilities can remain unnoticed in secondary artifacts long after the core project ships a patch.

What to Do Now: A Prioritized Action Plan

1. Inventory Every Apache Instance (High Priority)

Use asset management tools, cloud inventory APIs, and host-level commands to locate all Apache HTTP Server installations. Commands like httpd -v, apache2ctl -v, or package queries (rpm -qa | grep httpd, dpkg -l | grep apache) will reveal installed versions. Include ephemeral resources like CI runner containers that may only exist during builds.

2. Prioritize Public-Facing and Indirect-Mapping Servers

Any server reachable from the internet that uses AddType/AddHandler should be considered critical. Servers that extensively use Alias or RewriteRule to map requests to script directories are at heightened risk. Immediately apply mitigations or schedule patches.

3. Patch to Apache 2.4.62 or Later

For packages distributed through official channels, update to the latest build provided by your OS vendor. Ensure that the package version corresponds to upstream Apache 2.4.62 or higher. Do not stop at 2.4.61 if that is still available in your repositories—it contains only the partial fix.

4. Rebuild and Redeploy Container Images

If your containers embed Apache, rebuild your base images with a patched version and redeploy through your CI/CD pipeline. Do not rely on runtime upgrades inside long-running containers, as those can be overwritten or lost. Use image scanning to validate the patched layers before promotion.

5. Apply Configuration Hardening (If Immediate Patching Is Impossible)

If you cannot patch within 24–48 hours, take these short-term steps to reduce exposure:
- Replace AddType/AddHandler with SetHandler directives.
- Restrict file permissions so that the web server user cannot read source files they don’t need to serve.
- Use WAF rules or network ACLs to limit access to directories that contain sensitive scripts.
- Monitor logs for unusual 200 OK responses to script file requests (e.g., GET /index.php returning a non-HTML body).

6. Demand SBOMs and Scan Third-Party Images

For any Microsoft Marketplace image or appliance not explicitly attested by MSRC, request an SBOM from the publisher. In staging environments, run container vulnerability scanners against the image and look for Apache versions in the 2.4.60–2.4.61 range. Only deploy images that pass the scan or have a VEX statement confirming the fix.

7. Subscribe to MSRC’s CSAF/VEX Feeds

Microsoft’s new attestation feeds are machine-readable and can be integrated into vulnerability management platforms. As the program expands, they will automatically flag new product entries for the same CVE, reducing the need for manual hunting.

Outlook: Beyond Azure Linux

Microsoft’s move toward structured vulnerability disclosures is a net positive for defenders. CSAF and VEX documents provide clear, actionable statements of exploitability, and the company has committed to expanding coverage over time. The advisory for CVE-2024-39884 is an early example of that transparency.

However, the current gap between Azure Linux attestation and silent uncertainty around other products serves as a reminder that software supply chains are only as strong as their weakest inventory. Until every artifact is covered by a VEX statement, the burden falls on individual organizations to verify what they run.

The immediate takeaway is straightforward: patch your Azure Linux systems, but don’t stop there. Treat every Apache instance as potentially vulnerable until you have evidence—from a scan, an SBOM, or a vendor attestation—that it is not. The regression window is small, but the damage from a single source code leak can be immense.