CVE-2026-56862: 
cAdvisor Análisis y mitigación de vulnerabilidades

CVE-2026-56862 is a Denial of Service vulnerability in the Go standard library's crypto/tls package, caused by improper handling of TLS handshake messages such as KeyUpdate. Because these messages are always treated as state-advancing regardless of whether a handshake has been completed, a malicious client can flood a server with KeyUpdate messages, forcing it to perform key derivation operations indefinitely. Affected versions include crypto/tls before 1.25.13, 1.26.0–1.26.6, and 1.27.0-0–1.27.0-rc.3. It was published on August 13, 2026, with a CVSS v3.1 base score of 7.5 (High) (GitHub Advisory, Red Hat Bugzilla).

The root cause is classified under CWE-770 (Allocation of Resources Without Limits or Throttling) and CWE-1050 (Excessive Platform Resource Consumption within a Loop). The Go crypto/tls implementation incorrectly treats KeyUpdate handshake messages as always state-advancing, without verifying that the TLS handshake has been fully completed first. An unauthenticated remote attacker can exploit this by repeatedly sending KeyUpdate messages over a network connection, causing the server to continuously execute computationally expensive HKDF key derivation operations without any throttling or limit. The issue is tracked upstream as Go issue #80528 and fixed via code change CL 804261 (GitHub Advisory, Go Vuln DB).

Successful exploitation results in a Denial of Service against any Go application using the crypto/tls package as a TLS server. An unauthenticated attacker can exhaust server CPU resources by forcing continuous key derivation operations, degrading or completely disabling service availability. There is no impact on confidentiality or data integrity, and no lateral movement potential is associated with this vulnerability (GitHub Advisory, Red Hat Bugzilla).

No public proof-of-concept exploit code is known to exist, and there is no evidence of active in-the-wild exploitation as of the time of publication. The vulnerability is automatable (no user interaction or privileges required), making it straightforward for an attacker to trigger remotely at scale. The EPSS score is approximately 0.185–0.483%, indicating a low-to-moderate near-term exploitation probability. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog (GitHub Advisory, Go Vuln DB).

1. Reconnaissance: Identify internet-facing services built with Go that use TLS (e.g., HTTPS servers, gRPC services), targeting versions of the Go standard library before 1.25.13, 1.26.6, or 1.27.0-rc.3.
2. Establish TLS connection: Initiate a TLS connection to the target server. The handshake does not need to be completed for the attack to be effective, as the server processes KeyUpdate messages regardless of handshake state.
3. Send repeated KeyUpdate messages: Continuously transmit TLS KeyUpdate handshake messages to the server without completing or advancing the handshake. Each message triggers a key derivation operation on the server side.
4. Resource exhaustion: The server's CPU becomes saturated performing HKDF key derivation operations in response to the flood of KeyUpdate messages, degrading or denying service to legitimate clients (GitHub Advisory, Go Vuln DB).

• Network: Unusually high volume of TLS KeyUpdate handshake messages from a single or small set of source IPs; TLS connections that remain open without completing the handshake while generating high server load.
• System: Sustained high CPU utilization on Go-based TLS server processes without a corresponding increase in legitimate application traffic or request throughput.
• Logs: Application or system logs showing repeated TLS handshake-related operations or errors; Go runtime logs indicating excessive cryptographic key derivation activity.

Upgrade the Go toolchain to a fixed version: Go 1.25.13, Go 1.26.6, or Go 1.27.0-rc.3 or later, which correct the improper handling of KeyUpdate messages. As a temporary workaround, consider implementing rate limiting on incoming TLS connections or handshake messages at the network or load-balancer level to reduce exposure. Red Hat has issued an advisory (RHSA-2026:54836) and SUSE has released SUSE-SU-2026:3640-1 for affected distributions (GitHub Advisory, Red Hat Bugzilla, Go Vuln DB).

The Go security team disclosed the vulnerability via the golang-announce mailing list and published a fix through the standard Go release process. The issue was also discussed on the oss-security mailing list. Distribution vendors including Red Hat, SUSE, and openSUSE issued security advisories and patches shortly after disclosure. No significant independent researcher commentary or notable social media discussion has been identified beyond standard vulnerability tracking (golang-announce, Red Hat Bugzilla).