External risk intelligence

Unauthenticated Login Stack Overflow Leads to Remote Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-91843

The vulnerability exists in an unauthenticated login process. Services that expose authentication interfaces directly to the internet, such as gateways or remote access portals, are designed to be reachable and are commonly deployed as public-facing services.

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This critical vulnerability, identified in certain network-accessible systems, allows unauthenticated attackers to potentially execute arbitrary code with root privileges due to a stack overflow during the login process. The ease of exploitation and high potential impact warrant a review to understand our exposure to this type of threat.

Unauthenticated login flaw allows code execution.
Critical flaw impacts systems accessible externally.
Confirm relevance and assess our exposure.

Attack Path

How an attacker could exploit the issue

A remote attacker could exploit this vulnerability by sending specially crafted data to the login process, bypassing authentication. Because the vulnerability resides in the unauthenticated login, an attacker requires no prior access to the system. Successful exploitation could lead to arbitrary code execution with root privileges, potentially compromising the entire system.

No authentication required.
Triggered by specially crafted login data.
Enables remote code execution as root.

Live Threat

Current exploitation, exposure, and threat context

A stack overflow vulnerability in the unauthenticated login process could allow an attacker to execute arbitrary code remotely with root privileges. This may affect system data and the behavior of services when exposed externally and not adequately protected.

System data and services.
Network-based code execution.
Remote root privilege escalation.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in an unauthenticated login process allows remote code execution with root privileges, posing a critical risk. The first practical step is to identify all instances of the affected technology, confirm their internet reachability and business criticality, and then assign ownership for remediation planning.

Identify and assign the accountable owner.
Confirm external reachability and business impact.
Plan remediation based on validated risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the software affected by CVE-2026-91843?

CVE-2026-91843 affects network-accessible systems that manage authentication. These components are typically deployed as gateways or remote access portals to control user entry. Because they must be reachable to perform their function, they often sit at the edge of a network to verify credentials before allowing further system interaction.

How does this stack overflow vulnerability work?

This vulnerability is classified as CWE-121, or a stack-based buffer overflow. It occurs when the software's login process accepts more data than its memory buffer can hold, causing the extra data to overwrite adjacent memory. In this case, an attacker can manipulate this overwritten memory to force the system to execute their own unauthorized code with high-level root privileges.

Does any login activity trigger this CVE-2026-91843 flaw?

No. The vulnerability is triggered specifically when the system processes specially crafted data sent to the login interface. Normal login attempts using standard, legitimate credentials do not trigger this memory error. The flaw requires the attacker to send malicious data designed to exploit the specific buffer management error during the handshake.

How do I know if my systems are at risk?

Halo Surface Signal indicates this vulnerability is very likely to pose a risk because it exists in an unauthenticated login process. If your systems are internet-facing, such as gateways or remote access portals, they are designed to be reachable and are therefore at a higher risk of being targeted by remote actors.

What should I do first to address this risk?

Start by creating an inventory of all instances of the affected technology across your environment. Once you have identified them, confirm which ones are reachable from the internet and evaluate their business criticality. Use this information to assign ownership and begin planning your remediation steps.

References

support.checkpoint.com/results/sk/sk1000155

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.