CVE-2024-2004: Azure Linux Attestation Explained and Actions

Microsoft’s short public attestation — that “Azure Linux includes this open‑source library and is therefore potentially affected” — is accurate for the product it names, but it is a scoped inventory statement, not proof that no other Microsoft product could include the same vulnerable curl/libcurl code. m](Security Update Guide - Microsoft Security Response Center))

Background / Overview​

CVE‑2024‑2004 is a low‑severity logic bug in curl/libcurl that can cause a protocol explicitly disabled by a user to remain enabled in certain pathological command lines. The upstream curl project disclosed the bug on March 27, 2024 and fixed it in curl 8.7.0; affected upstream versions are 7.85.0 through 8.6.0 inclusive. The bug is unusual in that exploiting it requires constructing a deliberately self‑contradictory protocol argument (for example, using --proto with a set that disables all protocols and then attempting to remove some), which the curl team judged to be unlikely in practice.
Microsoft’s Security Response Center (MSRC) entry for the CVE — visible in the Microsoft Update Guide — includes a product‑scope note that Azure Linux images include the implicated open‑source library and are therefore potentially affected, and Microsoft says it will publish CSAF/VEX attestations and update the CVE mapping if additional Microsoft products are identified. That language is deliberate: it confie Linux while leaving open the possibility that other Microsoft artifacts could carry the same upstream code. (msrc.microsoft.com)
This article explains what that attestation does — and does not — mean, verifies the technical facts about the curl vulnerability using multiple independent sources, and provides practical guidance for administrators who need to answer the simple operational question: is Azure Linux the only Microsoft product that ships the vulnerable code?

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What CVE‑2024‑2004 actually is — technical verification​

The bug, succinctly​

• The root cause is a logic error in curl’s protocol selection parsing: when a user both disables and enables protocols in the same option set, an error path could leave the default allowed protocols active rather than honoring the user’s intent to disable them all. In short: an explicit “disable all” plus an attempted exclusion could still permit a disabled protocol to be used.
• The command-line proof of concept the curl team posted was:
  curl --proto -all,-http curl
  which would perform a plaintext HTTP request despite -http being present in the disable list. That construction is contrived — it explicitly disables every protocol then attempts to remove one from the disabled list — and the curl maintainers assessed the practical risk as low.

Versions and the fix (verified)​

• Affected upstream curl versions: 7.85.0 up to and including 8.6.0. Fixed in curl 8.7.0. This is confirmed by the curl project advisory and multiple independent vulnerability databases (NVD, Debian/Ubuntu trackers, OSV).
• Many downstream distributions issued patches or updated package releases shortly after the upstream fix; Azure Linux (Microsoft’s Linux distribution lineage) received its own curl package updates as part of its security updates. Independent scanner plugins and advisories (for example, Tenable/Nessus plugin entries) cite Azure Linux updates for the curl CVE.

Practical impact​

• The vulnerability is realistic only in highly specific conditions where an operator or script explicitly constructs a nonsensical protocol selection that disables every protocol. The upstream team classifies the bug as low severity and has no evidence of active exploitation. Nonetheless, because libcurl is embedded in many products and scripts, vendors and downstream distributors treated it seriously and issued fixes.

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What id — reading the attestation​

Microsoft’s phrasing on MSRC is operationally precise: it names Azure Linux as including the implicated package and therefore “potentially affected,” and commits to publishing machine‑readable CSAF/VEX attestations and updating the CVE mapping if other Microsoft products are found to ship the affected upstream component. That wording is intended as an inventory disclosure for the named product family rather than as a categorical exclusivity guarantee. (msrc.microsoft.com)
Key points to extract from Microsoft’s wording:

• **Authoritative yes for Azure Linspected Azure Linux artifacts and determined they include the upstream curl component that contained the flaw, so Azure Linux customers should treat the product as potentially affected until updates are applied.
• Not an assertion of global exclusivity: The statement does not say “only Azure Lisays Microsoft will update the CVE mapping if additional Microsoft products are found to include the component. Treat the attestation as an explicit yes for Azure Linux and as not yet assessed for other Microsoft SKUs.
• CSAF/VEX timeline and transparency: Microsoft has committed to publishing CSAF/VEX data (machine‑readable vulnerability/exposure information) for product families; that program improves traceability but does not instantly guarantee every artifact across a sprawling enterprise has been scanned. Microsoft’s note is consistent with that staged, product‑by‑product approach.

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Does Microsoft ship curl/libcurl in other products?​

Short answer: Microsoft ships or packages curl/libcurl in multiple contexts — but public attestations vary by product family. The presence, configuration, and build options of curl differ across those products, which affects whether a given upstream CVE is applicable.

Known Microsoft contexts that include curl or curl-derived code​

• Azure Linux (Azure’s Linux distro / CBL‑Mariner lineage) — explicitly attested by MSRC for this CVE. Administrators of Azure Linux images should assume the product is potentially affected and apply updates. (msrc.microsoft.com)
• Windows native curl.exe (C:\Windows\System32\curl.exe) — Windows ships a Microsoft‑built copy of curl in modern releases (Windows 10/Server 2019 and later). Microsoft maintains a custom build and, historically, has treated some upstream curl CVEs as “not applicable” to Windows when the Microsoft build omits the affected functionality (for example, when certain TLS stacks or protocol support are not included). Microsoft Q&A threads and community reporting inuilds sometimes differ in configuration (Schannel, HTTP/2, QUIC support) and that Microsoft may not push a separate, out‑of‑cycle curl binary for low‑severity upstream bugs. Vendors and users should not replace the built‑in curl.exe in Windows system paths without caution.
• WSL and Marketplace VM images — these are Linux distribution images; if they include a vulnerable upstream curl package, they may be affected in the same way as their distribution. Microsoft’s attestation for Azure Linux does not automatically cover third‑party or community Marketplace images or user‑installed packages inside VMs. Operators must scan the specific images and packages they run.
• Internal components, agents, SDKs, or third‑party software bundled by Microsoft — any Microsoft product that bundles an application using libcurl (for example, telemetry agents, CLI tools, or container images) could be affected if that binary links the vulnerable libcurl version. Microsoft’s initial CSAF/VEX program rollout focused on Azure Linux, and other product families may be assessed later. The absence of a public attestation is not proof of absence.

Why configuration matters​

Even when a product includes curl/libcurl, the precise build flags and the TLS backend matter. Several curl CVEs were non‑applicable on Windows because Microsoft’s build used the native Schannel TLS stack or omitted HTTP/2/QUIC features that were the attack vectors for some upstream bugs. For CVE‑2024‑2004 specifically, Microsoft’s public guidance for Windows in some internal channels characterized the issue as low severity and noted the impractical nature of the command‑line exploit, which influenced Microsoft’s decision‑making around shipping updated curl.exe binaries in Windows Update. Those statements are product‑specific risk assessments, not blanket statements about the library's presence.

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ttestation implies operationally​

For Azure Linux customers​

• Treat the Azure Linux CVE attestation as an authoritative inventory result: if you run Azure Linux images, check the installed curl/libcurl package version and apply the vendor patch or package update to obtain curl >= 8.7.0 (or the distribution’s fixed package). Tenable and distribution advisories list Azure Linux package updates for this CVE.

For crosoft products​

• Do not assume safety based on absence of a public MSRC attestation. If you run Windows endpoints, WSL, container images, or Microsoft agents:
• Inventory the actual binary and package versions present in your environment.
• Check whether the local curl.exe/libcurl is an MS‑built binary and whether the feature set (HTTP/2, QUIC, TLS backend) could make the upstream CVE applicable.
• Apply vendor guidance where Microsoft has published it; where Microsoft has not yet published a VEX for a product, treat it as “not yet assessed” rather than “not affected.”

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Strengths and limitations of Microsoft’s approach (critical analysis)​

Notable strengths​

• Product‑scoped transparency is practical: Microsoft’s decision to publish CSAF/VEX information for product families — startinis a strong step toward machine‑readable, verifiable supply‑chain transparency. It lets customers programmatically consume vulnerability mappings for specific product artifacts, which is invaluable for large scale operations. Microsoft explicitly committing to update CVE mappings when further products are confirmed improves traceability and reduces guesswork.
• Avoids false positives from blanket claims: By attesting only for products it has inventory‑checked, Microsoft decreases the risk of overstating impact. A blanket statement that every Microsoft product includes an upstream library would be both inaccurate and operationally useless. Microsoft’s scoped attestation gives customers a factual starting point they can act on immediately.

Material limitations and risks​

• Perception vs. reality gap: Product‑scoped attestations can be misread as “only this product is affected.” Many customers (and press headlines) will interpret Microsoft’s note as an exclusivity guarantee unless the nuance is emphasized — a dangerous misunderstanding for security teams that assume no further action is necessary. Several community threads show this exact confusion.
• Inventory latency: Microsoft’s product portfolio is large and heterogeneous. A staged CSAF/VEX rollout means that some Microsoft‑distributed artifacts may remain unassessed for weeks or months. During that window, customers must either perform independent scans or trust Microsoft’s patch cadence. That can be a problem for orgs with strict vulnerability SLAs.
• Build/feature differences complicate applicability: Even if a product bundles curl, differing build options (TLS stack, protocol support) make applicability of an upstream CVE nontrivial. Microsoft’s internal determinations about “not vulnerable” for certain Windows curl builds are legitimate, but they require clear public documentation to avoid leave‑behind confusion. Community posts show administrators asking for explicit clarifications on the Windows curl build and which CVEs apply.

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Practical guidance — what to do now​

Below are concrete, prioritized steps for security teams and operators dealing with CVE‑2024‑2004 and Microsoft’s attestation.

• Inventory first
• Locate curl/libcurl binaries and package versions across your estate — Linux images, Windows System32, WSL distributions, containers, and any Microsoft agents. Use automated software inventory and package-management queries where possible.
• Prioritize Azure Linux assets
• If you run Azure Linux images, assume they are potentially affected until you confirm the package version has been updated. Apply the distribution’s security updates or upgrade to the fixed package that includes the upstream 8.7.0 fix. Scanning rules (Tenable/Nessus, OS package trackers) will flag Azure Linux curl versions that are vulnerable.
• Check Windows built‑in curl.exe carefully
• Query C:\Wixe --version on representative hosts and compare build characteristics (libcurl version, TLS backend). Do not replace or overwrite Microsoft’s system curl binary without vendor guidance; instead, rely on Microsoft’s official update channels or documented mitigations. If Windows’ build omits the affected functionality, document the evidence. Microsoft Q&A and Windows support engineering responses have previously explained differences in builds that affect applicability.
• Scan application dependencies
• Many apps vendor or embed libcurl; container images and packaged agents are common places to find embedded vulnerabilities. Rebuild images with fixed libcurl or update packages in place.
• Apply compensating controls where appropriate
• If you cannot immediately patch, review scripts and automation thato arguments (or otherwise programmatically set protocol allow/deny lists). Avoid exposing scriptable surfaces that could pass a crafted --proto value from untrusted input.
• Automate and subscribe to machine‑readable feeds
• Consume vendor CSAF/VEX feeds and multiple distribution trackers (NVD, OSV, distro trackers) to detect when Microsoft or other vendors change attack applicability or publish new attestations. Microsoft’s CSAF program reduces friction when it’s available, but you should keep independence via your own supply‑chain controls.

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When to expect Microsoft to expand product mappings (and how to interpret future updates)​

Microsoft’s published process indicates they will update CVE entries and CSAF/VEX mappings if additional products are identified as shipping the vulnerable upstream component. Practically, that means:

• Microsoft will publish additional attestation lines per product family as inventory checks complete.
• Customers should treat newly added attestations as actionable: if MSRC adds a product to a CVE mapping, that product has beitream code and should be prioritized for remediation. (msrc.microsoft.com)

However, the absence of a Microsoft attestation for a product does not mean the product is safe — it may simply not yet have completed inventory scanning. For time‑sensitive remediation, rely on your own inventories and scanning to confirm whether a Microsoft product in your environment carries the vulnerable libcurl variant.

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Conclusion​

Microsoft’s statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is accurate and actionable for Azure Linux customers — but it is not a categorical guarantee that Azure Linux is the only Microsoft product that could contain the vulnerable curl/libcurl code. The upstream vulnerability (CVE‑2024‑2004) is a low‑severity logic error fixed in curl 8.7.0, and downstream vendors, including Microsoft for Azure Linux, have applied or signaled fixes. Multiple independent sources — the curl project advisory and NVD/OSV/distro trackers — confirm the affected versions and the fix.
Operationally, treat Azure Linux as confirmed for immediate remediation, inventory other Microsoft artifacts in your estate for curl/libcurl usage, and do not assume “no mention equals no effect.” Microsoft’s CSAF/VEX rollout improves transparency, but customers must continue to perform their own scans and maintain a defensible patching posture across mixed Microsoft and third‑party artifacts.
If you run Azure Linux images, patch the curl package now. If you run Windows or mixed environments, inventory the specific binaries and build features before concluding applicability; document the findings and follow vendor guidance. Those measured steps will ensure you close the loop between Microsoft’s product‑scoped attestation and the real exposure state inside your environment.

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Source: MSRC Security Update Guide - Microsoft Security Response Center