Apache HTTP Server Vulnerable to HTTP/2 Bomb Denial-of-Service Attack (CVE-2026-49975)
Apache HTTP Server versions 2.4.17 through 2.4.67 are susceptible to a denial-of-service vulnerability, CVE-2026-49975, allowing attackers to crash servers via specially crafted HTTP/2 requests.
A critical denial-of-service (DoS) vulnerability, identified as CVE-2026-49975, has been discovered in the Apache HTTP Server, affecting a wide range of versions from 2.4.17 up to 2.4.67. The flaw resides within the mod_http module, a core component responsible for handling HTTP requests and responses.
Exploitation of this vulnerability involves sending malicious HTTP/2 requests that trigger an excessive memory allocation within the server. The Apache HTTP Server's implementation of the HTTP/2 protocol, when processing certain malformed or resource-intensive requests, fails to adequately limit the memory consumed, leading to a resource exhaustion scenario. This can overwhelm the server's capacity to handle legitimate traffic, ultimately resulting in a denial of service.
The impact of a successful attack could be severe, rendering websites and online services hosted on vulnerable Apache servers inaccessible to legitimate users. Given the widespread use of Apache HTTP Server across the internet for hosting web applications and services, the potential attack surface is significant. Attackers could leverage this vulnerability to disrupt business operations, impact service availability, and potentially cause financial losses for affected organizations.
Fortinet's PSIRT has published details regarding this vulnerability, noting that it specifically impacts the mod_http component. While the primary vulnerability lies within Apache HTTP Server itself, Fortinet is investigating its potential impact on its own products, particularly those that may incorporate or rely on affected Apache versions. Products like FortiPAM and FortiProxy are listed as having specific versions affected, with recommendations to upgrade or migrate to fixed releases.
As of the advisory's publication, Apache HTTP Server versions 2.4.17 through 2.4.67 are confirmed to be vulnerable. Users are strongly advised to update to a patched version of Apache HTTP Server as soon as possible. For organizations using Fortinet products, specific upgrade paths and migration strategies are provided for affected versions of FortiPAM and FortiProxy, indicating the need for prompt action within those ecosystems as well.
This vulnerability highlights the ongoing challenges in securing complex network services, particularly those that handle high-volume network protocols like HTTP/2. The ability for attackers to cause a denial of service through resource exhaustion remains a potent threat, especially when targeting widely deployed software like the Apache HTTP Server. Organizations must maintain vigilance in applying security patches and monitoring for potential exploitation.
While the primary concern is denial of service, the nature of excessive memory allocation vulnerabilities can sometimes be a precursor or component of more complex attacks, though CVE-2026-49975 is currently classified and understood as a DoS issue. The prompt disclosure and advisories from vendors like Fortinet are crucial for enabling timely remediation and mitigating widespread impact.
This incident underscores the importance of keeping web server software up-to-date. The Apache Software Foundation regularly releases security updates, and administrators must prioritize the timely application of these patches to protect their infrastructure from known vulnerabilities. The specific versions affected, 2.4.17 through 2.4.67, represent a substantial range, emphasizing the need for a broad review of deployed Apache instances.