SB2026060491 - Resource exhaustion in Microsoft IIS HTTP/2 support

Description

This security bulletin contains information about 1 vulnerability.

1) Resource exhaustion (CVE-ID: CVE-2026-49975)

CWE-ID: CWE-400 - Resource exhaustion

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to uncontrolled resource consumption in the HTTP/2 request handling and HPACK header processing when handling crafted HTTP/2 requests that use repeated indexed header references and a stalled flow-control window. A remote attacker can send specially crafted HTTP/2 requests to cause a denial of service.

The issue is reachable in the default HTTP/2 configuration.

Remediation

Cybersecurity Help is not aware of any official remediation provided by the vendor.

References

• https://blog.calif.io/p/codex-discovered-a-hidden-http2-bomb
• https://github.com/califio/publications/tree/main/MADBugs/http2-bomb