Overview
The CVE-2026-26233 advisory describes a denial-of-service that arises when login requests are not rate-limited, allowing unauthenticated remote attackers to crash and restart the server via HTTP/2 single-packet flood with 100+ parallel login attempts. While this vulnerability was identified in Mattermost, the underlying class of weakness-Unrestricted Resource Consumption (CWE-400)-is broadly applicable to Go applications using the Gin framework. The real-world impact is severe: a flooded login surface consumes CPU, memory, and I/O resources until the service becomes unresponsive or crashes, impacting availability and user trust. This pattern can manifest in Go (Gin) apps when endpoints handling authentication or other high-entropy, user-driven operations are exposed without throttling, enabling resource exhaustion under adversarial conditions. The CVE highlights the risk of HTTP/2 flood attacks, where a single or few malformed frames can drive disproportionate load on the server if not mitigated by rate limiting and proper flow-control awareness.
Affected Versions
Mattermost 11.4.x <= 11.4.0; 11.3.x <= 11.3.1; 11.2.x <= 11.2.3; 10.11.x <= 10.11.11
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"net/http"
"time"
"sync"
"github.com/gin-gonic/gin"
"golang.org/x/time/rate"
)
type client struct {
limiter *rate.Limiter
lastSeen time.Time
}
var (
clients = make(map[string]*client)
mu sync.Mutex
)
func getLimiter(ip string) *rate.Limiter {
mu.Lock()
defer mu.Unlock()
if c, exists := clients[ip]; exists {
c.lastSeen = time.Now()
return c.limiter
}
l := rate.NewLimiter(5, 10) // 5 requests per second with a burst of 10
clients[ip] = &client{limiter: l, lastSeen: time.Now()}
return l
}
func rateLimitMiddleware() gin.HandlerFunc {
return func(c *gin.Context) {
ip := c.ClientIP()
limiter := getLimiter(ip)
if !limiter.Allow() {
c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{"error": "rate limit exceeded"})
return
}
c.Next()
}
}
// Vulnerable pattern: login endpoint without rate limiting
func loginVulnHandler(c *gin.Context) {
var cred struct {
Username string `json:"username"`
Password string `json:"password"`
}
if err := c.ShouldBindJSON(&cred); err != nil {
c.JSON(http.StatusBadRequest, gin.H{"error": "invalid payload"})
return
}
// Simulate workload; no rate limiting
time.Sleep(50 * time.Millisecond)
c.JSON(http.StatusOK, gin.H{"status": "login attempted", "user": cred.Username})
}
// Fixed pattern: same login logic but protected by per-IP rate limiting
func loginFixedHandler(c *gin.Context) {
var cred struct {
Username string `json:"username"`
Password string `json:"password"`
}
if err := c.ShouldBindJSON(&cred); err != nil {
c.JSON(http.StatusBadRequest, gin.H{"error": "invalid payload"})
return
}
time.Sleep(50 * time.Millisecond)
c.JSON(http.StatusOK, gin.H{"status": "login attempted", "user": cred.Username})
}
func main() {
r := gin.Default()
// Unthrottled endpoint for demonstration (Vulnerable)
r.POST("/login-vuln", loginVulnHandler)
// Throttled endpoint (Fixed) to mitigate resource exhaustion
r.POST("/login-fixed", rateLimitMiddleware(), loginFixedHandler)
r.Run(":8080")
}