Cache Poisoning

Cache Poisoning is a skill for Claude Code from allsmog/vuln-scout. It costs 64 tokens per session (3,188 once invoked), scanned A, original, MIT.

A security guide for finding cache poisoning and web cache deception. These are attacks where a proxy or content delivery network stores or serves the wrong web response, potentially exposing private content or changing what users receive.

In plain words
What is it for?
Use it when reviewing Nginx, Varnish, Cloudflare, or other proxy and CDN settings, checking static-file caching, investigating server-side request forgery data leaks, and reviewing authenticated content exposure.
Why use it?
It helps uncover risks that ordinary code checks may miss in caching rules, cache keys, and the handling of logged-in responses.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the vuln-scout plugin — 32 skills, 15 commands, 9 agents shipped together

Good fit Use it when reviewing Nginx, Varnish, Cloudflare, or other proxy and CDN settings, checking static-file caching, investigating server-side request forgery data leaks, and reviewing authenticated content exposure.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/allsmog/vuln-scout/cache-poisoning
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add allsmog/vuln-scout --skill cache-poisoning
Clone the repo
git clone --depth 1 https://github.com/allsmog/vuln-scout

Made for: Claude Code.

Or install vuln-scout, the plugin that ships this one along with the rest of its 32 skills, 15 commands, 9 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for Cache Poisoning

README.md
[![agentmods](https://agentmods.dev/badge/skills/allsmog/vuln-scout/cache-poisoning/github.svg)](https://agentmods.dev/skills/allsmog/vuln-scout/cache-poisoning)
Your own site
<a href="https://agentmods.dev/skills/allsmog/vuln-scout/cache-poisoning"><img src="https://agentmods.dev/badge/skills/allsmog/vuln-scout/cache-poisoning/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for Cache Poisoning

Your own site · 80×15
<a href="https://agentmods.dev/skills/allsmog/vuln-scout/cache-poisoning"><img src="https://agentmods.dev/badge/skills/allsmog/vuln-scout/cache-poisoning.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 64 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,188 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00064 $0.03188
Opus 5 $0.00032 $0.01594
Sonnet 5 $0.00013 $0.00638
Haiku 4.5 $0.00006 $0.00319

Measured 11d ago against content hash 7602987c0982, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

Cache Poisoning scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 11d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

grep -rniE "requests\.get|http\.Get|fetch\(|axios\.|urllib" --include="*.py" --include="*.go" --include="*.js" --include="*.ts"
vuln-scout/skills/cache-poisoning/SKILL.md · 409 lines

How it starts

The opening of the file, as written. The whole thing — 409 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Cache Poisoning & Web Cache Deception

Purpose

Provide detection patterns for HTTP cache poisoning and web cache deception vulnerabilities, including proxy cache misconfigurations, cache key manipulation, and authenticated response caching.

OWASP Top 10 Mapping

Category: Related to A01 (Broken Access Control), A05 (Security Misconfiguration)

CWEs:

  • CWE-524: Use of Cache Containing Sensitive Information
  • CWE-525: Use of Web Browser Cache Containing Sensitive Information
  • CWE-444: Inconsistent Interpretation of HTTP Requests
  • CWE-436: Interpretation Conflict

When to Use

Activate this skill when:

  • Reviewing proxy/CDN configurations (Nginx, Varnish, Cloudflare, etc.)
  • Analyzing SSRF vulnerabilities for exfiltration vectors
  • Auditing applications with static file caching
  • Looking for authenticated content exposure
  • Checking cache key construction for manipulation

Web Cache Deception

Overview

Web cache deception occurs when:

  1. Proxy caches responses based on file extension (e.g., .png, .css)
  2. Application serves dynamic content regardless of path extension
  3. Attacker tricks victim into visiting /profile.png
  4. Proxy caches authenticated response
  5. Attacker retrieves cached sensitive data

Detection Patterns

Nginx Cache Configuration
# Find proxy cache configurations
grep -rniE "proxy_cache|proxy_cache_valid|proxy_cache_key" --include="*.conf" --include="nginx.conf"

# Check cache rules for static extensions (HIGH RISK)
grep -rniE "location.*\.(css|js|png|jpg|jpeg|gif|ico|svg|woff)" -A10 --include="*.conf" | grep -iE "proxy_cache|cache"

# Cache key analysis - look for missing user identification
grep -rniE "proxy_cache_key" --include="*.conf"

# Caching authenticated responses (CRITICAL if no Vary header)
grep -rniE "proxy_cache_valid\s+200" --include="*.conf"
Varnish Cache Configuration
# VCL cache rules
grep -rniE "vcl_recv|vcl_hash|vcl_backend_response" --include="*.vcl"

# Static extension caching
grep -rniE "req\.url.*\.(css|js|png|jpg|jpeg|gif|ico)" --include="*.vcl"

# Cache TTL settings
grep -rniE "set beresp\.ttl|beresp\.grace" --include="*.vcl"

Read the full file on GitHub · 409 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 11d ago First seen · 409 lines · 64 tokens per session scan A 7602987c0982

Subscribe to this mod's changes

Cache Poisoning is a skill published in the GitHub repository allsmog/vuln-scout (24 stars, last pushed 3mo ago), licensed MIT. It adds 64 tokens to every session and 3,188 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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