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 UnboundCompute/security-agent-skills --skill auditing-session-lifecycle-and-fixationgit clone --depth 1 https://github.com/UnboundCompute/security-agent-skillsWrote 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/unboundcompute/security-agent-skills/auditing-session-lifecycle-and-fixation)<a href="https://agentmods.dev/skills/unboundcompute/security-agent-skills/auditing-session-lifecycle-and-fixation"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-session-lifecycle-and-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/unboundcompute/security-agent-skills/auditing-session-lifecycle-and-fixation"><img src="https://agentmods.dev/badge/skills/unboundcompute/security-agent-skills/auditing-session-lifecycle-and-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 | $0.00190 | $0.02131 |
| Opus 5 | $0.00095 | $0.01066 |
| Sonnet 5 | $0.00038 | $0.00426 |
| Haiku 4.5 | $0.00019 | $0.00213 |
Grade A, and why
auditing-session-lifecycle-and-fixation scanned grade A with 0 findings 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 10d 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 141 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Auditing session lifecycle and fixation: whether a session is rotated, scoped, and destroyed
A session identifier can be perfectly random and still be a bug, because the attack is not guessing it but controlling its lifecycle. If the identifier issued to an anonymous visitor survives unchanged into their authenticated session, an attacker who planted it now holds that session; if logout clears only the client cookie, a captured identifier stays valid; if nothing expires, a stolen identifier lives forever. This audit assumes the identifier is unguessable, that is a separate concern, and asks whether it is rotated at the right moments, invalidated when it should be, timed out, and scoped so only the right party can hold it. You audit it by reading the login, privilege-change, and logout paths and the cookie attributes, against the framework's session defaults. The discipline is checking those defaults first, because the rotation or the attribute is often set centrally, not at the call site.
When to use
- You are reviewing authentication, logout, or session-management code, or the cookie attributes it sets.
- You want to know whether a session can be fixated, replayed after logout, or held indefinitely.
- The identifier is already assumed unguessable and you are auditing its lifecycle, not its entropy.
Scope check
Exercise session handling only against applications and accounts you own or are authorized to assess; a fixation or replay demonstration rides a real user's authenticated session. Use test accounts and coordinate. If you can't name the authorization, stop.
The loop
- Establish the framework's session defaults first. Determine what the framework does on its own: whether session-fixation protection regenerates the identifier at login by default, whether the session cookie's secure, http-only, and same-site attributes come from a global cookie policy or a gateway, and whether the server session store enforces its own timeout. These defaults decide what a missing call at the handler means, so settle them before flagging anything.
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.
- 10d ago First seen · 141 lines · 190 tokens per session scan A 534cb9874540
auditing-session-lifecycle-and-fixation is a skill published in the GitHub repository UnboundCompute/security-agent-skills (5 stars, last pushed yesterday), licensed MIT. It adds 190 tokens to every session and 2,131 once invoked, about $0.0010 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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