# CVE-2026-15308: Incremental HTMLParser feed() allows CPU-exhaustion DoS via repeated unterminated markup declarations
> Attackers can cause CPU exhaustion and denial of service in applications using Python's HTMLParser by sending repeated unterminated markup declarations.
- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Jul 2026
- **Updated:** 13 Aug 2026
- **Also known as:** ALPINE-CVE-2026-15308, ALSA-2026:39183, ALSA-2026:39320, ALSA-2026:39771, ALSA-2026:39798, ALSA-2026:39893, ALSA-2026:40856, ALSA-2026:41949, AZL-109701, AZL-92271, BELL-CVE-2026-15308, BIT-libpython-2026-15308, BIT-python-2026-15308, BIT-python-min-2026-15308, CLSA-2026-1784019126, CLSA-2026-1784019434, CLSA-2026-1784036547, CLSA-2026-1784070836, CLSA-2026-1784071323, CLSA-2026-1784072295, CLSA-2026-1784110083, CLSA-2026-1784110442, CLSA-2026-1784126834, CLSA-2026-1784137549, CLSA-2026-1784188935, CLSA-2026-1784218124, CLSA-2026-1784218371, CLSA-2026-1784270796, CLSA-2026-1784280875, CLSA-2026-1784297320, CLSA-2026-1784713418, CLSA-2026-1784713911, CLSA-2026-1784798087, CLSA-2026-1784798441, CLSA-2026-1784798564, CLSA-2026-1784798816, CLSA-2026-1784798883, CLSA-2026-1784799167, CLSA-2026-1786707590, DEBIAN-CVE-2026-15308, ECHO-ddd3-d328-2db3, GHSA-7qj2-q5c8-cxx5, MINI-5825-c5x3-6mv2, MINI-6cv3-h6mc-9hrw, MINI-7grw-h2m7-h6mw, MINI-9683-7wp9-4mrq, MINI-h373-2x6g-qvvj, PSF-2026-33, RHSA-2026:37533, RHSA-2026:37535, RHSA-2026:39183, RHSA-2026:39320, RHSA-2026:39771, RHSA-2026:39798, RHSA-2026:39893, RHSA-2026:40856, RHSA-2026:41949, RHSA-2026:47939, RHSA-2026:50064, RHSA-2026:50065, RHSA-2026:50770, RHSA-2026:50771, RHSA-2026:50816, RLSA-2026:39183, RLSA-2026:39320, RLSA-2026:39771, RLSA-2026:39798, RLSA-2026:39893, RLSA-2026:40856, RLSA-2026:41949, ROOT-OS-ALPINE-320-CVE-2026-15308, ROOT-OS-DEBIAN-11-CVE-2026-15308, ROOT-OS-DEBIAN-12-CVE-2026-15308, ROOT-OS-DEBIAN-13-CVE-2026-15308, UBUNTU-CVE-2026-15308
## What is CVE-2026-15308?
CVE-2026-15308 is a high-severity denial of service vulnerability in Python Python, published on 9 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
### Official description
The incremental HTML parser (html.parser.HTMLParser) allows for CPU
denial-of-service through repeated unterminated markup declarations when
processing uncontrolled data.
Weakness: CWE-400 (Uncontrolled Resource Consumption)
## Which versions are affected by CVE-2026-15308?
3 open source packages ship an affected version, including libpython, python and python-min. It affects 1 product.
| Package | Ecosystem | 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 |
| `python-unversioned-command` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-debug` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-devel` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-idle` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-libs` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-test` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3-tkinter` | AlmaLinux:10 | All versions | 3.12.13-2.el10_2.1 |
| `python3.14` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-debug` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-devel` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-debug` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-devel` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-idle` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-libs` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-test` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-freethreading-tkinter` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-idle` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-libs` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-test` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `python3.14-tkinter` | AlmaLinux:10 | All versions | 3.14.5-1.el10_2.1 |
| `platform-python` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `platform-python-debug` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `platform-python-devel` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `python3-idle` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `python3-libs` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `python3-test` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `python3-tkinter` | AlmaLinux:8 | All versions | 3.6.8-77.el8_10.alma.1 |
| `python3.12` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-debug` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-devel` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-idle` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-libs` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-rpm-macros` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-test` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
| `python3.12-tkinter` | AlmaLinux:8 | All versions | 3.12.13-3.el8_10 |
Products: Python Python.
## How do I fix CVE-2026-15308?
Upgrade libpython to a fixed version for your release line: 3.10.21, 3.11.16, 3.12.14 or 3.13.15.
## Is CVE-2026-15308 being exploited?
There is no known exploitation of CVE-2026-15308 in the wild and no public exploit code.
## Other vulnerabilities in Python Python
- [CVE-2008-5031](https://insights.sbomify.com/CVE-2008-5031/): Integer overflow in n/a (critical 10.0)
- [CVE-2014-4650](https://insights.sbomify.com/CVE-2014-4650/): Path traversal in n/a (critical 9.8)
- [CVE-2016-5636](https://insights.sbomify.com/CVE-2016-5636/): Integer overflow in n/a (critical 9.8)
- [CVE-2007-4559](https://insights.sbomify.com/CVE-2007-4559/): Path traversal in n/a (critical 9.8)
- [CVE-2017-17522](https://insights.sbomify.com/CVE-2017-17522/): Command injection in n/a (high 8.8)
## Fix prompt for AI coding agents
```text
Check this codebase for CVE-2026-15308 and fix it if it is affected.
What it is: CVE-2026-15308 is a high-severity denial of service vulnerability in Python Python, published on 9 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-15308 in the wild and no public exploit code.
Affected packages and fixed versions:
- libpython (Bitnami): affected all versions; fixed in 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7
- python (Bitnami): affected all versions; fixed in 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7
- python-min (Bitnami): affected all versions; fixed in 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2026-15308/ (Markdown: https://insights.sbomify.com/CVE-2026-15308/index.md)
```
## Sources
- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15308
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15308
- OSV: https://osv.dev/vulnerability/CVE-2026-15308
---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-15308/
Summaries are generated and may contain mistakes; the official description above is the record.