CVE-2024-2756 is a practical reminder that a terse vendor mapping — “Azure Linux includes this open‑source library and is therefore potentially affected” — is an attestation of scope, not a categorical guarantee that no other Microsoft product could ship the same vulnerable code.
CVE-2024-2756 is a PHP-level vulnerability that arises from a partial fix to an earlier issue tracked as CVE-2022-31629. In short, the bug lets an attacker cause PHP to treat a standard, insecure cookie as though it carried the restrictive Host- or Secure- prefix semantics, undermining protections intended to ensure cookies are sent only on secure channels and only for a single host. The defect is language/runtime parsing logic: malformed or specially crafted cookie names or parameters can bypass server‑side expectations and cause PHP to accept and treat an insecure cookie as secure. This class of weakness enables session hijacking and CSRF escalation in scenarios where applications rely exclusively on prefix semantics for cookie safety.
Multiple independent vulnerability trackers have cataloged CVE‑2024‑2756 and its impact across Linux distributions and PHP releases. Distributors such as Amazon Linux, Oracle Linux and several mainstream Linux vendors published advisories and package updates after patches were released upstream; commercial vulnerability scanners (Nessus/Tenable) added checks to identify vulnerable PHP packages inside Azure Linux images. These external mappings corroborate the vulnerability description and the fixed versions published by the upstream PHP project.
Microsoft’s public advisory language for this CVE — the sentence quoted by the user — is the operational touchpoint that generated questions: the vendor explicitly names Azure Linux as a product that “includes this open‑source library and is therefore potentially affected,” while committing to expand the product mapping later if additional Microsoft products are found to ship the component. That phrasing is deliberate and consistent with Microsoft’s phased, artifact‑level CSAF/VEX rollout: start with an inventoryable product (Azure Linux) and publish machine‑readable attestations before broadening coverage. (msrc.microsoft.com)
Crucially, that sentence is not a proof of exclusivity. Microsoft explicitly promises to update the CVE mapping if it discovers the same component in additional Microsoft products. In practice, large vendors inventory and attest product families iteratively; they frequently publish attestation data for a subset of products first and extend coverage over time. The absence of an attestation for a particular Microsoft SKU does not equal technical absence of the upstream component.
Longer, precise answer:
The practical guidance is simple and operational: patch Azure Linux now, scan and inventory all Microsoft artifacts you run, and do not assume absence of evidence equals evidence of absence. Microsoft’s public commitment to expand CSAF/VEX mappings over time helps, but until inventories are complete the safest posture is verification and remediation under a defense‑in‑depth policy. (msrc.microsoft.com)
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
CVE-2024-2756 is a PHP-level vulnerability that arises from a partial fix to an earlier issue tracked as CVE-2022-31629. In short, the bug lets an attacker cause PHP to treat a standard, insecure cookie as though it carried the restrictive Host- or Secure- prefix semantics, undermining protections intended to ensure cookies are sent only on secure channels and only for a single host. The defect is language/runtime parsing logic: malformed or specially crafted cookie names or parameters can bypass server‑side expectations and cause PHP to accept and treat an insecure cookie as secure. This class of weakness enables session hijacking and CSRF escalation in scenarios where applications rely exclusively on prefix semantics for cookie safety.Multiple independent vulnerability trackers have cataloged CVE‑2024‑2756 and its impact across Linux distributions and PHP releases. Distributors such as Amazon Linux, Oracle Linux and several mainstream Linux vendors published advisories and package updates after patches were released upstream; commercial vulnerability scanners (Nessus/Tenable) added checks to identify vulnerable PHP packages inside Azure Linux images. These external mappings corroborate the vulnerability description and the fixed versions published by the upstream PHP project.
Microsoft’s public advisory language for this CVE — the sentence quoted by the user — is the operational touchpoint that generated questions: the vendor explicitly names Azure Linux as a product that “includes this open‑source library and is therefore potentially affected,” while committing to expand the product mapping later if additional Microsoft products are found to ship the component. That phrasing is deliberate and consistent with Microsoft’s phased, artifact‑level CSAF/VEX rollout: start with an inventoryable product (Azure Linux) and publish machine‑readable attestations before broadening coverage. (msrc.microsoft.com)
What the vulnerability actually does — technical summary
- The vulnerability is an input‑parsing/normalization bug in PHP’s cookie handling code that accepts an insecure Set‑Cookie header or cookie name and maps it into PHP’s cookie array as if it had the Host- or Secure- semantics.
- The root cause is a partial upstream fix for CVE‑2022‑31629: the original patch closed some paths but left parsing corner cases open. Attackers can exploit those remaining paths when they can influence HTTP responses (network‑level attacker, malicious intermediary, or same‑site script scenarios).
- The real‑world impact is session integrity loss: an attacker who can make a victim store an attacker‑controlled cookie that PHP will honor as a secure cookie can inject session identifiers or perform CSRF-style actions that rely on cookie presence/semantics.
Parsing Microsoft’s wording: what “Azure Linux includes this open‑source library” actually means
Microsoft’s short single‑sentence mapping is a product‑scoped inventory result: it says Microsoft inspected the Azure Linux distribution artifacts and found the upstream component that is associated with CVE‑2024‑2756. That is an authoritative, actionable signal for customers who run Azure Linux images — they should treat those images as in‑scope and apply the vendor‑recommended updates. It is also visible and machine‑readable for organizations that consume Microsoft’s CSAF/VEX attestations. (msrc.microsoft.com)Crucially, that sentence is not a proof of exclusivity. Microsoft explicitly promises to update the CVE mapping if it discovers the same component in additional Microsoft products. In practice, large vendors inventory and attest product families iteratively; they frequently publish attestation data for a subset of products first and extend coverage over time. The absence of an attestation for a particular Microsoft SKU does not equal technical absence of the upstream component.
Is Azure Linux the only Microsoft product that could be affected?
Short answer: No — not necessarily.Longer, precise answer:
- Azure Linux is the only Microsoft product that Microsoft has publicly attested (so far) to include the implicated PHP component for CVE‑2024‑2756. That attestation is authoritative for that product family. (msrc.microsoft.com)
- However, that attestation does not demonstrate that other Microsoft products or internal artifacts cannot — or do not — ship the same vulnerable PHP runtime or library. Without a comprehensive, artifact‑level inventory that includes every Microsoft image, appliance, SaaS runtime, Marketplace image and internal build artifact, absence of a public mapping cannot be relied upon as evidence of absence. Microsoft’s own advisory language commits to expanding mappings if more artifacts are found.
- the exact package/version shipped inside that artifact,
- packaging choices and configuration (what modules are installed, compiled, or trimmed),
- whether upstream fixes were backported into vendor builds,
- whether the artifact uses an independent runtime (for example, a Microsoft image that embeds a vendor PHP runtime vs one that relies on a distribution package).
Which Microsoft artifacts could plausibly contain PHP (and therefore deserve verification)?
I will not assert that any of these do contain the vulnerable component; instead, this is an explicit checklist of artifact types where PHP commonly appears and that organizations should inventory and verify:- Azure Linux images (Microsoft’s attestation covers this family explicitly; apply the Azure Linux PHP updates).
- CBL‑Mariner derivatives — Azure Linux lineage or any internal Microsoft container base images that are derived from Mariner may carry the same packages.
- Marketplace images and published VM images — some Marketplace VM images include LAMP stacks or preinstalled PHP packages. Those are user‑scoped but distributed by Microsoft or partners.
- Azure App Service / Web Apps (Linux) — the platform can host PHP and may provision specific runtime images. Investigate which runtime image is used for an App Service instance (managed runtime vs user container).
- Azure Functions / managed serverless runtimes — if you are running functions using custom containers or if the platform provides a PHP runtime, verify the runtime image.
- WSL/Windows‑hosted PHP installs — customers who run PHP under WSL or on Windows Server/IIS (via PHP for Windows) should verify the Windows/WSL PHP package versions.
- Marketplace container images and third‑party distributions included in Azure Marketplace where PHP appears in the stack (these might be built by partners).
- Developer/CI images published by Microsoft (build agents, developer VMs) that might include PHP runtime tooling.
How to verify whether a given Microsoft artifact contains the vulnerable PHP component
Operational steps defenders should take to move from doubt to evidence:- Inventory your Microsoft‑supplied artifacts.
- List all Azure Marketplace images, custom images, App Service runtime selections, and any Microsoft‑hosted container images you run.
- Inspect package versions inside images or instances.
- For RPM‑based images: rpm -qa | grep -i php or dnf list installed 'php*'
- For DEB‑based images: dpkg -l | grep php
- For containers: docker run --rm -it <image> sh -c "php -v || rpm -qa | grep php || dpkg -l | grep php"
- Check php -v output and compare to fixed upstream releases (the upstream advisory and vendor advisories list the patched versions). If you cannot run php directly, inspect package metadata or image manifests.
- For managed platform services (App Service, Functions) query the runtime configuration: validate which base image or runtime version your service uses and then check that runtime image separately.
- Use automated scanning tools across your environment: Trivy, Nessus, Qualys, or vendor patch reporting can detect known vulnerable PHP packages inside images — Tenable/Nessus published a plugin specifically for Azure Linux updates for CVE‑2024‑2756 as part of standard checks.
- Consult Microsoft’s machine‑readable VEX/CSAF for CVE mappings (if present). If Microsoft has published CSAF/VEX records, they will list artifact‑level attestations that can speed triage; but remember the attestation set may be incomplete and should not be the sole source of truth. (msrc.microsoft.com)
- Update to the vendor‑supplied patched package immediately, or
- Replace the runtime image with one that carries the patched PHP build, or
- Apply mitigations (see below) until you can patch.
Recommended mitigations and defense‑in‑depth
Patch quickly, but also apply layered mitigations because runtime patch windows can vary across managed platforms:- Apply the upstream patches: upgrade to the patched PHP releases (the upstream advisory lists fixed versions; vendors provide patched package builds). This is the primary fix.
- Harden cookie handling in application code: do not rely solely on prefix semantics. Validate cookie names and attributes server‑side and reject unexpected cookie name formats. Reject cookies that do not meet your expected secure/path/domain attributes before honoring session cookies.
- Limit exposure for session establishment: require TLS for session establishment and reject session tokens over insecure channels in server logic.
- WAF / edge rules: implement Web Application Firewall rules to drop suspicious Set‑Cookie headers or to observe and block anomalous cookie naming patterns where feasible.
- Control the runtime image supply chain: require signed base images or image provenance checks in CI/CD so you can ensure runtime images use approved, patched package sets.
- Detection: log and alert when unexpected cookie names appear in inbound requests; monitor for cookie values that differ across requests and for session anomalies typical of cookie injection attacks.
- Inventory automation: integrate package scanning into your CI pipeline and use vulnerability scanning to detect drift (e.g., updated images that introduced vulnerable packages). Tenable/Nessus and other scanners already ship checks for CVE‑2024‑2756 across major distributions.
Critical analysis: strengths, limits and supply‑chain implications
- Strengths:
- Microsoft’s product‑level attestation is useful: it gives Azure Linux operators a binary, actionable signal to patch and reduces time‑to‑triage for that product family. Microsoft’s commitment to publish machine‑readable CSAF/VEX attestations is a material improvement in vendor transparency. That approach scales well for customers who can automate based on product mappings. (msrc.microsoft.com)
- Upstream and distribution vendors moved to patch releases and vendors such as Amazon Linux, Oracle and others published advisories, enabling a broad set of fixes across the ecosystem. Multiple independent trackers (NVD, Zend, AquaSec) confirm the same technical picture.
- Limits and risks:
- The practical limit is coverage. An attestation for Azure Linux helps Azure Linux customers, but until Microsoft completes artifact‑level inventories across all product families, customers who run other Microsoft artifacts must perform their own verification. The attestation model is iterative; until Microsoft lists every artifact, silence cannot be treated as safety.
- Supply‑chain ambiguity: the same upstream component can appear in multiple derivative artifacts (VM images, platform runtimes, Marketplace images). Vendors often backport or repackage upstream fixes differently; this variability makes centralized, one‑line product statements insufficient for defenders who operate heterogeneous fleets.
- Operational friction: App Service and other managed platform users often lack direct access to base image internals. For those customers, vendor advisories plus the vendor’s CVE mapping are the only signals. Where mappings are absent, customers need vendor guidance or must assume risk until the vendor confirms. Microsoft’s promise to update CVE entries if more products are found helps, but it is a promise that depends on the vendor’s internal inventories and release timelines.
- Unverifiable claims to flag:
- Any definitive statement that other specific Microsoft products are affected (for example, “Azure App Service was affected”) is unverifiable in the absence of an explicit Microsoft attestation or published artifact inventory. Where Microsoft has not published an attestation for a product family, the correct posture is to assume potential exposure and verify artifact inventories, rather than rely on silence. Microsoft’s own advisory language makes this nuance explicit: it states Azure Linux is affected and that the vendor will update the CVE if additional products are discovered to contain the component. (msrc.microsoft.com)
Practical checklist for defenders (quick reference)
- If you run Azure Linux: apply the Azure Linux PHP updates Microsoft published for CVE‑2024‑2756 immediately. Use your distro update tooling and reboot where required.
- For all Microsoft‑hosted artifacts in your environment:
- Inventory them (Marketplace images, App Service runtimes, Functions, WSL, custom images).
- Inspect installed PHP package versions (rpm/dpkg/php -v).
- If you find affected versions, upgrade to vendor‑patched packages or replace the runtime image.
- Apply application‑level cookie validation as a short‑term mitigation.
- Enable WAF/edge controls to limit exposure where possible.
- Subscribe to and monitor vendor CSAF/VEX feeds and MSRC update pages for updates to the CVE mapping; Microsoft committed to update CVE entries when additional impacted products are found. (msrc.microsoft.com)
What to watch next
- Watch Microsoft’s CVE/VEX/CSAF attestations for this CVE: if Microsoft discovers the component in additional product families it will update the advisory and the machine‑readable attestations accordingly. Until then, treat Azure Linux as confirmed and other Microsoft artifacts as unverified and worthy of active inspection. (msrc.microsoft.com)
- Upstream PHP advisories and distributor security advisories (Amazon Linux, Oracle Linux, Red Hat, Ubuntu) will continue to be primary sources for patch versions; ensure those updates are rolled into the images and artifacts you run.
- Vulnerability scanners and image‑inventory tooling will continue to refresh detection rules for this CVE; integrate their output into your patch‑and‑deploy workflow to catch drift. Tenable/Nessus and other major scanners added Azure Linux checks for this CVE shortly after public disclosure.
Conclusion
Microsoft’s statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is authoritative and actionable for Azure Linux customers — it reflects a completed inventory for that product family and should prompt immediate patching. However, that wording is not a technical guarantee that no other Microsoft product can or does ship the same vulnerable PHP component. Defensive teams must treat the Microsoft attestation as a starting point, not an endpoint: inventory every relevant Microsoft artifact in your environment, verify PHP package versions, apply upstream patches, and adopt short‑term mitigations where necessary.The practical guidance is simple and operational: patch Azure Linux now, scan and inventory all Microsoft artifacts you run, and do not assume absence of evidence equals evidence of absence. Microsoft’s public commitment to expand CSAF/VEX mappings over time helps, but until inventories are complete the safest posture is verification and remediation under a defense‑in‑depth policy. (msrc.microsoft.com)
Source: MSRC Security Update Guide - Microsoft Security Response Center
