CVE-2026-18503 Super-linear CPU usage for unbounded input to csv.Sniffer.sniff()
Attackers can cause excessive CPU consumption in applications using Python's csv.Sniffer by providing unbounded input, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-18503?
CVE-2026-18503 is a low-severity denial of service vulnerability in CPython, published on 10 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
Attacker-controlled CSV samples can trigger super-linear regular-expression work during dialect sniffing and consume significant CPU when applications pass unbounded input to csv.Sniffer.sniff().
Weakness: CWE-1176
Which versions are affected by CVE-2026-18503?
3 open source packages ship an affected version, including libpython, python and python-min.
| Package | Affected | Fixed in |
|---|---|---|
libpython Bitnami | All versions | 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7 |
python Bitnami | All versions | 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7 |
python-min Bitnami | All versions | 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7 |
Linux distribution packages (7)
python3.10 Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-debug Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-devel Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-idle Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-libs Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-test Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
python3.10-tkinter Red Hat:hummingbird:1 | All versions | 0:3.10.21-1.hum1 |
How do I fix CVE-2026-18503?
Upgrade libpython to a fixed version for your release line: 3.10.21, 3.11.16, 3.12.14 or 3.13.15.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-18503 being exploited?
There is no known exploitation of CVE-2026-18503 in the wild and no public exploit code.
Sources
Also known as AZL-95586, AZL-95619, BELL-CVE-2026-18503, BIT-libpython-2026-18503, BIT-python-2026-18503, BIT-python-min-2026-18503 and 11 more.