External risk intelligence

Apache HTTP Server mod_http2 Use After Free Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-57941

The Apache HTTP Server is a ubiquitous, public-facing web server designed to host websites and APIs. The mod_http2 module handles HTTP/2 traffic directly at the network edge, making it inherently exposed to the public internet as part of the standard deployment pattern for web infrastructure.

Use After Free

Apache Http Server

2.4.0 to before 2.4.69

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

A Use After Free vulnerability in the Apache HTTP Server's mod_http2 module could allow unauthenticated attackers to compromise server availability and integrity. This critical issue, which affects versions from 2.4.0 through 2.4.68, is particularly concerning due to the widespread use of Apache as a public-facing web server. The primary concern at this level is to confirm if this technology is in use and assess any potential exposure.

Flaw in web server's HTTP/2 handling.
Affects common, public-facing web infrastructure.
Confirm relevance and assess exposure.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by sending specially crafted requests to a vulnerable Apache HTTP Server. This targets the `mod_http2` module, specifically a re-entrancy issue within shared session data. Successful exploitation could lead to a denial-of-service condition or potentially allow for arbitrary code execution, depending on the specific conditions and how the use-after-free is triggered.

Unauthenticated network access required.
Triggered by HTTP/2 requests to `mod_http2`.
Risk of denial-of-service or code execution.

Live Threat

Current exploitation, exposure, and threat context

A use-after-free vulnerability in Apache HTTP Server's mod_http2 could allow an attacker to cause a denial-of-service or potentially execute arbitrary code by exploiting a re-entrancy issue within shared session data. This could affect the availability and integrity of services hosted by the server.

Server availability and integrity.
Network requests exploit re-entrancy.
Unpredictable service disruption or code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This Use After Free vulnerability in Apache HTTP Server's mod_http2 impacts systems running versions 2.4.0 through 2.4.68. Infrastructure and platform teams responsible for web servers are likely to own remediation. The immediate first step is to identify all instances of the affected Apache HTTP Server, confirm their exposure and criticality, and then coordinate with the appropriate application or system owners to plan a controlled update.

Infrastructure and platform teams own remediation.
Verify affected Apache HTTP Server instances.
Plan and coordinate controlled updates.

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 role of Apache HTTP Server in web infrastructure?

Apache HTTP Server is a widely deployed, open-source platform designed to host websites and APIs. It serves as foundational software that processes incoming web traffic at the network edge. This ubiquity makes it a primary component in modern web service architecture, where modules like mod_http2 manage high-efficiency data exchange.

How is the CVE-2026-57941 vulnerability defined?

This vulnerability is identified as a Use After Free error, categorized under CWE-416. It occurs when software continues to access a memory location after it has been freed. In this specific instance, the issue originates from a re-entrancy flaw involving shared session data within the mod_http2 module.

Can this vulnerability be triggered by any network request?

Not every request triggers this flaw. The vulnerability requires specifically crafted requests targeting the mod_http2 module's session management. While it does not require authentication, it is scoped specifically to the handling of shared session data and re-entrancy conditions rather than general server operations.

Why is this issue highly relevant to web security?

According to the Halo Surface Signal, the mod_http2 module is inherently exposed to the public internet because it handles HTTP/2 traffic at the network edge. Given the server's role in hosting critical web infrastructure, this vulnerability presents a significant risk to service availability and integrity.

What are the recommended steps to manage this risk?

Organizations should first perform an inventory of all instances running Apache HTTP Server versions 2.4.0 through 2.4.68. Once affected systems are identified, infrastructure and platform teams must coordinate a controlled update to a secure version to resolve the underlying memory management defect.

References

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.