Researchers have found three vulnerabilities in the popular Zoom meeting platform that could let one meeting participant attack another through malicious collaboration data.

The vulnerabilities, tracked as CVE-2026-53413, CVE-2026-53414, and CVE-2026-53415, affect the code Zoom uses to process annotation data shared during meetings. The researchers named the set of flaws “Zoomsday.”

Affected applications are:

• Zoom Workplace on all supported platforms before version 7.1.5 and 7.0.6, depending on the release branch
• Zoom Workplace VDI Client for Windows before versions 7.0.11 and 6.6.16, depending on the release branch
• Zoom Rooms on all supported platforms before version 7.1.5
• Zoom Meeting SDK on all supported platforms before version 7.1.5

What can happen

What this means is that someone in the same Zoom meeting could send data that the Zoom app was not prepared to handle. Instead of simply displaying a drawing, text box, or other annotation, a vulnerable client could be tricked into crashing, leaking information, or even running attacker-controlled code.

Annotation features sound simple, but the underlying process is not. Your Zoom client receives structured data from another participant and turns that data into an object it can display on screen. According to the research, the annotation parser contained several memory-safety bugs. Like any software that processes data supplied by a third party, it has to be very careful about validating lengths, counts, and references before using them.

Remarkably, there is a discrepancy between the severity ratings assigned by the researchers, who rated them as Critical, and Zoom, which rated them as High.

The difference appears to come down to how the vulnerabilities are scored under the Common Vulnerability Scoring System (CVSS score). Zoom considers successful exploitation to require user interaction.

In practice, an attacker would first need to get into the same meeting as the intended victim. That could mean joining an open meeting, abusing a leaked meeting link, posing as an expected attendee, or compromising an account that already has access. Zoom considers it user interaction if the attacker persuades the target to join a meeting with the intent to compromise their machine.

How to stay safe

Zoom has published a security bulletin explaining which programs need to be updated and where to find the fixed versions.

To protect yourself from Zoomsday and have safe meetings:

• Update Zoom to the latest version as soon as possible.
• Restrict who can join your Zoom meetings. Use passcodes, waiting rooms, authenticated-user restrictions, and unique meeting links for sensitive calls.
• If features like annotation, whiteboards, remote control, file transfer, or third-party apps are not needed, consider turning them off, especially for meetings that have an open invitation nature.
• One crashed meeting is not proof of an attack, but if it happens on a regular basis, it’s worth investigating.
• Use an up-to-date, real-time anti-malware solution to block malicious code on your devices.
• Organizations should also check their device-management tools to make sure every deployed Zoom client is receiving updates.

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Zoom patched four security vulnerabilities, including two remote code execution bugs in the annotator function. Update your Zoom clients now.

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The post Zoom Patches Four Security Flaws, Including Two Remote Code Execution Bugs appeared first on Daily CyberSecurity.

Zoom patches a zero-click flaw that could let a meeting participant execute code on another user’s computer through the annotation feature.

Zoom has patched four vulnerabilities, including a critical zero-click flaw, tracked as CVE-2026-53413, in its annotation feature. CVE-2026-53413 is a memory corruption issue found by A Security that could allow a meeting participant to execute code on another participant’s computer.

Due to its impact, the researchers dubbed the flaw “Zoomsday,” it affects Zoom clients on all supported platforms and is linked to the proprietary protocol used by the annotation function. Zoom has now begun rolling out security updates to address the issue.

“Ⓐ Security, the Autonomous Offensive Security and Remediation Platform, discovered a critical flaw in Zoom that let an attacker take complete control of another user’s device during a live call. No click, no download, and nothing required of the victim but being in the meeting.” reads the report published by A Security. “The vulnerability is present in every version of Zoom on every device and operating system: Windows, Mac, iPhone, Android and Linux. The vulnerability exists in all versions up to and including 7.0.5.”

The flaw can corrupt memory through a specially crafted message. Attackers could exploit it to target meeting participants, execute code without user interaction, steal data, activate cameras or microphones, and install malware.

“A Research was able to exploit the fact that every Zoom client automatically parses whatever it receives, sending a specially crafted message to corrupt the receiving client’s memory and run code on it.” continues the advisory. “The protocol opens a direct channel between a viewer and a sharer, letting the attacker target each participant individually.”

Attackers could join or host a Zoom meeting and silently take control of participants’ devices without any user interaction. Once compromised, they could steal data, activate microphones or cameras, or install malware. In large meetings, a single malicious message could expose multiple participants at once.

Zoom’s Android client was chosen as a target because it is closed-source, widely deployed, and exposes a large native-code attack surface. Researchers first ranked 3,762 functions across 70 libraries, but found the JNI-focused approach missed remotely reachable code. Dynamic tracing instead identified libannotate.so and its proprietary annotation protocol.

Reverse engineering showed that annotation objects are serialized and rebuilt from attacker-controlled network data without adequate origin checks. Researchers discovered CVE-2026-53413, a remotely triggerable stack buffer overflow in CAnnoFormatBlock::Deserialize. A wire-controlled count can exceed fixed 128-byte buffers, allowing data to overwrite adjacent memory. The flaw can be reached through Zoom’s normal encrypted transport, requiring no victim interaction or instrumentation.

A Security also found CVE-2026-53414, a missing bounds check in Zoom’s annotator that can cause a buffer overread and crash a meeting participant’s client, enabling DoS attacks. It also identified CVE-2026-53415, a use-after-free flaw, but Zoom had already discovered the issue before A Security reported it.

“Because a zero-click RCE requires no user interaction, we prioritized giving customers time to receive both the client patch and the server-side mitigation before publishing.” concludes the report. “This post follows that coordinated timeline, and we are releasing it alongside CVE assignment,” A Security notes.

This week, Zoom released Workplace versions 7.1.5 and 7.0.6, Rooms version 7.1.5, and Meeting SDK version 7.1.5 for all supported platforms to address the above vulnerabilities.

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Pierluigi Paganini

(SecurityAffairs – hacking, Zoomsday)