CVE-2026-22776 is a vulnerability classified under CWE-409 (Improper Handling of Highly Compressed Data) affecting the yhirose cpp-httplib, a widely used C++11 single-file header-only HTTP/HTTPS library. The flaw exists in versions prior to 0.30.1 and stems from the library's inadequate validation of decompressed HTTP request body sizes. While cpp-httplib enforces a maximum payload length check against the compressed data size received over the network, it does not impose any limits on the size of the data after decompression. Attackers can exploit this by sending specially crafted HTTP requests with highly compressed payloads that decompress into very large data blobs, causing excessive memory allocation. This results in a Denial of Service condition due to resource exhaustion, potentially crashing or severely degrading the availability of services relying on the library. The vulnerability is remotely exploitable without any authentication or user interaction, increasing its risk profile. Although no known exploits have been reported in the wild, the CVSS 4.0 base score of 8.7 (high severity) reflects the significant impact and ease of exploitation. The vulnerability affects all systems using vulnerable versions of cpp-httplib in their HTTP/HTTPS handling, particularly those exposed to untrusted network traffic with compressed content encodings such as gzip or Brotli (br).

For European organizations, the primary impact is service disruption due to Denial of Service attacks exploiting this vulnerability. Organizations using cpp-httplib in web servers, APIs, or embedded devices that process compressed HTTP requests may experience crashes or degraded performance, leading to downtime and potential loss of business continuity. This can affect sectors relying on real-time or high-availability services such as finance, telecommunications, healthcare, and critical infrastructure. The vulnerability does not directly compromise confidentiality or integrity but can be leveraged as part of multi-stage attacks to cause operational disruption. Given the remote and unauthenticated nature of the exploit, attackers can launch large-scale DoS campaigns with minimal effort. The absence of known exploits in the wild suggests limited current active threat but does not preclude future exploitation, especially as the vulnerability becomes publicly known. Organizations failing to patch or mitigate this issue risk increased exposure to service outages and reputational damage.

The most effective mitigation is to upgrade cpp-httplib to version 0.30.1 or later, where the vulnerability is addressed by properly limiting decompressed data sizes. For organizations unable to immediately upgrade, implementing network-level controls to restrict or block HTTP requests with suspicious or unusually large compressed payloads can reduce exposure. Application-layer filtering to validate decompressed payload sizes before processing is recommended if feasible. Additionally, deploying Web Application Firewalls (WAFs) with custom rules to detect and block anomalous compression patterns can help mitigate exploitation attempts. Monitoring system memory usage and setting resource limits on processes using cpp-httplib can provide early detection and containment of DoS conditions. Regular security assessments and code reviews of third-party libraries should be conducted to identify and remediate similar risks proactively.