Spring Security CVE-2026-59276

Exploitation requires the attacker to be positioned on a low-latency network path to the target endpoint - same cloud VPC, shared Kubernetes node, or internal network - because internet-grade jitter drowns out the nanosecond-scale timing signal. The vulnerability activates on any Spring Security code path that compares a security-sensitive string (CSRF token, bearer token, or equivalent) using the affected equals() logic; no special non-default configuration is required beyond the application using one of the affected Spring Security versions. The CVSS PR:N metric confirms no authentication is required to attempt exploitation. Exploitation is limited by: (1) AC:H - requires controlled, low-jitter network conditions; (2) the need to issue a very large number of requests without triggering rate limits or anomaly detection; (3) no integrity or availability impact - only confidentiality of compared secrets is at risk.

The CVSS 3.1 vector (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N) scores 5.9 Medium, and this calibration is accurate: the AC:H reflects the genuine practical difficulty of executing timing attacks reliably across the public internet, where network jitter, JVM garbage collection pauses, load balancer variability, and OS thread scheduling all introduce noise orders of magnitude larger than the timing signal being measured. Exploitation is far more tractable in co-located or containerized environments - Kubernetes pods sharing a node, microservices on the same cloud VPC, or internal SOA deployments - where latency variance is suppressed. No EPSS data was supplied, and absence from CISA KEV indicates no confirmed active exploitation at time of analysis. POC status is unknown. SSVC dimensions: exploitation is none/public (no confirmed weaponized use), the attack is not trivially automatable at scale due to the measurement requirements, and technical impact is partial to total on confidentiality depending on what secrets are compared. Even a security team at a mid-sized organization should treat this as a scheduled-patch priority - not emergency response - unless the deployment processes extremely high-value authentication material (e.g., OAuth signing keys) in a low-latency network segment where timing oracle conditions are achievable.

An attacker with network access to a Spring Security-protected endpoint that validates a secret token (e.g., a CSRF token or API bearer token) sends thousands of crafted requests, each varying the candidate token by one character position, and records the statistical distribution of response times for each candidate. Over many iterations - feasible in a same-VPC or low-latency deployment - the attacker identifies which character at each position produces the longest average comparison time, progressively reconstructing the valid token without ever having authenticated. No public proof-of-concept exploit code was identified at time of analysis.