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.
npx skills add SecurityTalent/bugskill-ai --skill session-fixationgit clone --depth 1 https://github.com/SecurityTalent/bugskill-aiWrote 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.
[](https://agentmods.dev/skills/securitytalent/bugskill-ai/session-fixation)<a href="https://agentmods.dev/skills/securitytalent/bugskill-ai/session-fixation"><img src="https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/session-fixation/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.
<a href="https://agentmods.dev/skills/securitytalent/bugskill-ai/session-fixation"><img src="https://agentmods.dev/badge/skills/securitytalent/bugskill-ai/session-fixation.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00116 | $0.02089 |
| Opus 5.5 | $0.00046 | $0.00836 |
| Sonnet 5.5 | $0.00023 | $0.00418 |
| Haiku 4.5 | $0.00012 | $0.00209 |
Grade A, and why
session-fixation scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 20d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
PRE_TOKEN=$(curl -s -c /tmp/pre_cookies.txt "https://TARGET/login" \ How it starts
The opening of the file, as written. The whole thing — 170 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Session Fixation and Session Token Exposure
What Is Broken and Why
Session fixation occurs when an application authenticates a user but retains the pre-authentication session token rather than issuing a fresh one. An attacker who plants a known token (via URL parameter, XSS, or network manipulation) can then authenticate as the victim by using that same token once the victim logs in. Session token exposure extends the attack surface by allowing tokens to be harvested from HTTP traffic, proxy logs, browser history, and caches when tokens are transmitted without encryption or appear in GET request URLs. Predictable session tokens that can be forged complete the trifecta of session management failures.
Key Signals
- Application does not set a new
Set-Cookieheader upon successful authentication - Pre-login session token remains usable in authenticated requests post-login
- Session ID appears in URL query string:
?JSESSIONID=...or?session=... - Session ID transmitted over HTTP (not HTTPS) at any point
Set-CookielacksSecureflag on session cookiesSet-CookielacksHttpOnlyflag on session cookies- Session cookies set without
SameSiteattribute - Session ID predictable: sequential, timestamp-based, or short (< 50 chars / < 128-bit entropy)
Cache-Controlheaders on authenticated pages do not includeno-store- ASP.NET Forms Authentication cookies (
.ASPXAUTH) used without server-side session store Set-Cookie: __Host-or__Secure-prefixes absent (weaker binding guarantees)
Methodology
- Pre-auth token capture: Visit the login page without authenticating; record all cookies
issued (note
Set-Cookieheaders, cookie names, values). - Authentication with token intact: Submit valid credentials while preserving the pre-login
cookie; inspect response for
Set-Cookieheaders. - Fixation test: If no new session cookie issued, the pre-auth token has been elevated to an authenticated session — fixation confirmed.
- Forced cookie test: Using two accounts (attacker + victim), perform the 9-step forced cookie scenario: snapshot pre-login cookies, authenticate as victim, restore pre-login snapshot, attempt authenticated action, then swap and authenticate as attacker using victim's pre-login cookies.
- Token randomness analysis: Collect 50+ session tokens under identical conditions within a 50ms window; load into Burp Sequencer for statistical analysis.
- Transport exposure: Force HTTP access after authentication; observe if session cookie
is transmitted. Check for
Secureflag. - GET parameter exposure: Review all URLs and server logs for session IDs in query strings.
- Cache exposure: Check
Cache-Control,Pragma, andExpiresheaders on authenticated responses.
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.
- 20d ago First seen · 170 lines · 116 tokens per session scan A be6f2c58b892
session-fixation is a skill published in the GitHub repository SecurityTalent/bugskill-ai (13 stars, last pushed 21d ago), licensed MIT. It adds 116 tokens to every session and 2,089 once invoked, about $0.0005 per session on Opus 5.5. 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 2026-09-27.
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