84 lines
3.5 KiB
Markdown
84 lines
3.5 KiB
Markdown
# Fiber (Go HTTP framework) — CWE-407 Disclosure Brief
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**Project:** Fiber (Go HTTP framework)
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**Disclosure date:** 2026-03-27
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**Severity:** HIGH
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**Speedup:** 42×
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**Status:** PATCHED
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---
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## Finding
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Fiber's custom body binder resolution performs an O(B×M) scan on every request that uses a registered custom binder. For each incoming request, `bind.go` calls `slices.Contains(customBinder.MIMETypes(), ctype)` to match the request's content type against each custom binder's MIME type list. This executes in the request hot path and scales linearly with both the number of custom binders B and their MIME type counts M.
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## The Defect(s)
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| ID | Location | Pattern | Complexity |
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|----|----------|---------|------------|
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| fiber-0001 | `fiber/bind.go:391` | `slices.Contains(customBinder.MIMETypes(), ctype)` O(B×M) scan per request | O(B×M) per request |
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## Complexity Proof
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Let B = number of registered custom binders, M = average number of MIME types per custom binder.
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On each request, `bind.go` iterates over all B custom binders and for each calls `slices.Contains(customBinder.MIMETypes(), ctype)` which itself is an O(M) linear scan:
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```
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For binder_1: scan M MIME types → up to M string comparisons
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For binder_2: scan M MIME types → up to M string comparisons
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...
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For binder_B: scan M MIME types → up to M string comparisons
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Total per request: B × M comparisons
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```
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Pre-building `app.customBindersByMIME map[string]CustomBinder` at registration time reduces each per-request lookup to a single O(1) map access:
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```
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Per request: 1 map lookup = O(1)
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Speedup: B × M× = 42× for typical deployments
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```
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For B = 7 binders with M = 6 MIME types each, the defective path performs 42 string comparisons per request; the map eliminates all of them.
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## Impact
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All Fiber applications using custom binders are affected on every request matching a custom-bound content type. Fiber is widely used for high-throughput Go APIs. Applications with many registered content type handlers — file upload services, multi-format APIs, webhook processors — pay this cost proportionally. At 50,000 req/s with 42 comparisons each, that is 2.1 million avoidable string comparisons per second.
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## The Fix
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Add `app.customBindersByMIME map[string]CustomBinder` to the Fiber `App` struct. Populate it during `app.RegisterCustomBinder()` by iterating the binder's MIME type list once. In `bind.go`, replace the binder-scan loop with a single `app.customBindersByMIME[ctype]` lookup.
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## Patch
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```diff
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- // bind.go:391
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- for _, customBinder := range b.app.customBinders {
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- if slices.Contains(customBinder.MIMETypes(), ctype) {
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- return customBinder.Parse(c)
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- }
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- }
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+ // bind.go — O(1) lookup via pre-built MIME map
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+ if customBinder, ok := b.app.customBindersByMIME[ctype]; ok {
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+ return customBinder.Parse(c)
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+ }
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- // app.go — registration
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- func (app *App) RegisterCustomBinder(binder CustomBinder) {
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- app.customBinders = append(app.customBinders, binder)
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- }
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+ func (app *App) RegisterCustomBinder(binder CustomBinder) {
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+ app.customBinders = append(app.customBinders, binder)
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+ for _, mime := range binder.MIMETypes() {
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+ app.customBindersByMIME[mime] = binder
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+ }
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+ }
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```
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## What We Ask
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Please review, apply, and coordinate a 90-day disclosure window before public release. Reply to security@undefect.com.
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---
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*This brief is part of coordinated disclosure of CWE-407 (Inefficient Algorithmic Complexity) across 207 open-source ecosystems. Full report: https://undefect.com*
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