CVE-2023-44487

A flaw was found in handling multiplexed streams in the HTTP/2 protocol. A client can repeatedly make a request for a new multiplex stream and immediately send an RST_STREAM frame to cancel it. This creates extra work for the server setting up and tearing down the streams while not hitting any server-side limit for the maximum number of active streams per connection, resulting in a denial of service due to server resource consumption. Red Hat has rated the severity of this flaw as ‘Important’ as the US Cybersecurity and Infrastructure Security Agency (CISA) declared this vulnerability an active exploit. CVE-2023-39325 was assigned for the Rapid Reset Attack in the Go language packages. Security Bulletin https://access.redhat.com/security/vulnerabilities/RHSB-2023-003

Mitigation

Users are strongly urged to update their software as soon as fixes are available.
There are several mitigation approaches for this flaw.

1. If circumstances permit, users may disable http2 endpoints to circumvent the flaw altogether until a fix is available.
2. IP-based blocking or flood protection and rate control tools may be used at network endpoints to filter incoming traffic.
3. Several package specific mitigations are also available.
a. nginx: <https://www.nginx.com/blog/http-2-rapid-reset-attack-impacting-f5-nginx-products/&gt;
b. netty: <https://github.com/netty/netty/security/advisories/GHSA-xpw8-rcwv-8f8p&gt;
c. haproxy: <https://www.haproxy.com/blog/haproxy-is-not-affected-by-the-http-2-rapid-reset-attack-cve-2023-44487&gt;
d. nghttp2: <https://github.com/nghttp2/nghttp2/security/advisories/GHSA-vx74-f528-fxqg&gt;
e. golang: The default stream concurrency limit in golang is 250 streams (requests) per HTTP/2 connection. This value may be adjusted in the golang.org/x/net/http2 package using the Server.MaxConcurrentStreams setting and the ConfigureServer function which are available in golang.org/x/net/http2.