fix(message): prevent segfault on invalid UTF-8 - #624
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Check `PyUnicode_FromString()` results for attribute names and referrals to avoid NULL pointer dereferences.
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During fuzzing, two segfaults were found in LDAPmessage_to_python() due to unchecked failures from PyUnicode_FromString(). Other uses of PyUnicode_FromString() in this function already check for NULL before using the returned object. Valgrind logs were captured against python-ldap 3.4.5. The current main branch exhibits the same crash behavior.
Although such malformed UTF-8 is not expected from a compliant LDAP server, untrusted server input should not be able to crash the Python interpreter.
1. PyDict_Contains
LDAPmessage_to_python() did not check the return value of PyUnicode_FromString(attr). Invalid UTF-8 in an attribute name therefore resulted in a NULL pointer being passed to PyDict_Contains(), crashing the interpreter.
A part of valgrind log:
2. Py_DECREF
LDAPmessage_to_python() did not check the return value of PyUnicode_FromString() for referral URLs. Invalid UTF-8 therefore left refstr == NULL; after the ignored PyList_Append() failure, Py_DECREF(refstr) crashed the interpreter.
A part of valgrind log:
Reproduction script
#!/usr/bin/env python3 import socket import threading import time import ldap # msgid=1, SearchResultEntry: DN="", one attribute, type="\x93", empty value set ENTRY = bytes([ 0x30, 0x10, # SEQUENCE, len 16 0x02, 0x01, 0x01, # msgid = 1 0x64, 0x0b, # [APP 4] SearchResultEntry, len 11 0x04, 0x00, # DN = "" 0x30, 0x07, # attributes SEQUENCE, len 7 0x30, 0x05, # attr SEQUENCE, len 5 0x04, 0x01, 0x93, # type = "\x93" (invalid UTF-8) 0x31, 0x00, # vals SET (empty) ]) # msgid=1, SearchResultReference: single URL "\x93" REF = bytes([ 0x30, 0x08, # SEQUENCE, len 8 0x02, 0x01, 0x01, # msgid = 1 0x73, 0x03, # [APP 19] SearchResultReference, len 3 0x04, 0x01, 0x93, # URL = "\x93" ]) DONE = bytes([ 0x30, 0x0c, 0x02, 0x01, 0x01, 0x65, 0x07, 0x0a, 0x01, 0x00, 0x04, 0x00, 0x04, 00, ]) def serve(srv): conn, _ = srv.accept() conn.recv(4096) conn.sendall(REF + DONE) # another error place # conn.sendall(ENTRY + DONE) time.sleep(2) conn.close() def main(): srv = socket.socket() srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) srv.bind(("127.0.0.1", 0)) srv.listen(1) threading.Thread(target=serve, args=(srv,), daemon=True).start() conn = ldap.initialize(f"ldap://127.0.0.1:{srv.getsockname()[1]}/") conn.search_ext_s("dc=example,dc=com", ldap.SCOPE_SUBTREE, "(objectClass=*)", ["*"]) print("no crash — bug fixed?") if __name__ == "__main__": main()