Overview
CVE-2026-44242 describes an Unrestricted Resource Consumption vulnerability in the Micronaut framework where a cache (bundleCache) is keyed by Locale derived from the HTTP Accept-Language header. Before the fix in 4.10.22, an unauthenticated attacker could exhaust heap memory by sending requests with a huge number of unique Accept-Language values, each creating a distinct entry in an unbounded cache. This memory growth led to denial of service as the server consumed more and more heap space. The CVE is categorized under CWE-400: Uncontrolled Resource Consumption. While this CVE relates to a Java JVM framework, the pattern is a classic example of how user-controlled input can drive unbounded caching and memory usage in web services. In Go with the Gin framework, a similar failure mode occurs when developers cache per-user or per-request resources keyed on user-controlled headers or parameters without a bounded cache or eviction policy.
In real Go (Gin) services, the vulnerability manifests when a handler caches translations, templates, or other per-locale data keyed by Accept-Language (or other request headers) using an unbounded in-memory map. Attackers can craft a large set of distinct header values to enlarge the cache without limit, causing rapid memory growth, increased GC pressure, and eventually an Out-Of-Memory or DoS condition. This guide demonstrates both the vulnerable pattern (unbounded caching) and a remediation approach (bounded, eviction-enabled cache plus input limits) in Go, aligned with the same vulnerability class described by CVE-2026-44242.
Remediation focuses on preventing unbounded growth by introducing a bounded cache with eviction (LRU/LFU), applying sensible input size limits for headers, and avoiding retention of user-controlled inputs in memory. Do not cache content using arbitrary user input as the key without bounding the cache. Where possible, offload cache storage to an external system with explicit capacity planning, TTL, or use per-request generation rather than caching all combinations. This approach aligns with the CVE pattern and provides practical protections for Go (Gin) services.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"container/list"
"fmt"
"net/http"
"sync"
"github.com/gin-gonic/gin"
)
// Vulnerable cache: unbounded in-memory map keyed by Accept-Language
var vulnerableCache = make(map[string]string)
// Simple translation stub
func getTranslation(lang string) string {
return fmt.Sprintf("translation for %s", lang)
}
type entry struct {
key string
value string
}
type LRUCache struct {
capacity int
ll *list.List
cache map[string]*list.Element
mu sync.Mutex
}
func NewLRU(cap int) *LRUCache {
return &LRUCache{capacity: cap, ll: list.New(), cache: make(map[string]*list.Element)}
}
func (c *LRUCache) Get(key string) (string, bool) {
c.mu.Lock()
defer c.mu.Unlock()
if ele, ok := c.cache[key]; ok {
c.ll.MoveToFront(ele)
return ele.Value.(entry).value, true
}
return "", false
}
func (c *LRUCache) Put(key, value string) {
c.mu.Lock()
defer c.mu.Unlock()
if ele, ok := c.cache[key]; ok {
ele.Value = entry{key, value}
c.ll.MoveToFront(ele)
return
}
ele := c.ll.PushFront(entry{key, value})
c.cache[key] = ele
if c.ll.Len() > c.capacity {
back := c.ll.Back()
if back != nil {
ent := back.Value.(entry)
delete(c.cache, ent.key)
c.ll.Remove(back)
}
}
}
func main() {
r := gin.Default()
// Vulnerable endpoint: unbounded per-language cache
r.GET("/greet-vuln", func(c *gin.Context) {
lang := c.GetHeader("Accept-Language")
if lang == "" {
lang = "en-US"
}
if res, ok := vulnerableCache[lang]; ok {
c.String(http.StatusOK, res)
return
}
res := getTranslation(lang)
vulnerableCache[lang] = res
c.String(http.StatusOK, res)
})
// Fixed endpoint: bounded cache with eviction and header length cap
fixed := NewLRU(100)
r.GET("/greet-fixed", func(c *gin.Context) {
lang := c.GetHeader("Accept-Language")
if lang == "" {
lang = "en-US"
}
if len(lang) > 128 {
lang = lang[:128]
}
if v, ok := fixed.Get(lang); ok {
c.String(http.StatusOK, v)
return
}
res := getTranslation(lang)
fixed.Put(lang, res)
c.String(http.StatusOK, res)
})
r.Run(":8080")
}