# CVE-2019-9517: Denial of service in n/a

> Attackers can cause denial of service in HTTP/2 servers by exploiting unconstrained internal data buffering via manipulated TCP and HTTP/2 windows.

- **Severity:** High 7.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Aug 2019
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2019-9517, CLEANSTART-2026-VK65361, CLEANSTART-2026-XC13093, CLEANSTART-2026-XM65075, DEBIAN-CVE-2019-9517, GHSA-w6v5-q8c8-52xx, RHSA-2019:2893, UBUNTU-CVE-2019-9517

## What is CVE-2019-9517?

CVE-2019-9517 is a high-severity denial of service vulnerability in Apache Http Server, published on 13 Aug 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Some HTTP/2 implementations are vulnerable to unconstrained interal data buffering, potentially leading to a denial of service. The attacker opens the HTTP/2 window so the peer can send without constraint; however, they leave the TCP window closed so the peer cannot actually write (many of) the bytes on the wire. The attacker then sends a stream of requests for a large response object. Depending on how the servers queue the responses, this can consume excess memory, CPU, or both.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2019-9517?

It affects 23 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `httpd` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-devel` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-filesystem` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-manual` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-tools` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `httpd-tools-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_http2` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.11.3-3.module+el8.0.0+4096+eb40e6da |
| `mod_http2-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.11.3-3.module+el8.0.0+4096+eb40e6da |
| `mod_http2-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.11.3-3.module+el8.0.0+4096+eb40e6da |
| `mod_ldap` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_ldap-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_md` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_md-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_proxy_html` | Red Hat:enterprise_linux:8::appstream | All versions | 1:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_proxy_html-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 1:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_session` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_session-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_ssl` | Red Hat:enterprise_linux:8::appstream | All versions | 1:2.4.37-12.module+el8.0.0+4096+eb40e6da |
| `mod_ssl-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 1:2.4.37-12.module+el8.0.0+4096+eb40e6da |

Products: Apache Http Server, Apache Traffic Server, Apple Swiftnio, Canonical Ubuntu Linux, Debian Debian Linux, Fedoraproject Fedora, Mcafee Web Gateway, Netapp Clustered Data Ontap, Nodejs Node.js, Opensuse Leap, Oracle Communications Element Manager, Oracle Graalvm, Oracle Instantis Enterprisetrack, Oracle Retail Xstore Point of Service, Redhat Enterprise Linux, Redhat Jboss Core Services, Redhat Jboss Enterprise Application Platform, Redhat Openshift Service Mesh, Redhat Quay, Redhat Software Collections and 3 more.

## How do I fix CVE-2019-9517?

Apply the vendor's patch.

## Is CVE-2019-9517 being exploited?

There is no known exploitation of CVE-2019-9517 in the wild and no public exploit code.

## Other vulnerabilities in Apache Http Server

- [CVE-2021-42013](https://insights.sbomify.com/CVE-2021-42013/): Apache HTTP Server Path Traversal (critical 9.8, exploited in the wild)
- [CVE-2024-38475](https://insights.sbomify.com/CVE-2024-38475/): Apache HTTP Server Improper Escaping of Output (critical 9.1, exploited in the wild)
- [CVE-2021-40438](https://insights.sbomify.com/CVE-2021-40438/): Apache HTTP Server-Side Request Forgery (SSRF) (critical 9.0, exploited in the wild)
- [CVE-2019-0211](https://insights.sbomify.com/CVE-2019-0211/): Apache HTTP Server Privilege Escalation (high 7.8, exploited in the wild)
- [CVE-2021-41773](https://insights.sbomify.com/CVE-2021-41773/): Apache HTTP Server Path Traversal (high 7.5, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-9517 and fix it if it is affected.

What it is: CVE-2019-9517 is a high-severity denial of service vulnerability in Apache Http Server, published on 13 Aug 2019. 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-2019-9517 in the wild and no public exploit code.

Affected product: Apache Http Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2019-9517/ (Markdown: https://insights.sbomify.com/CVE-2019-9517/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-9517
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-9517
- OSV: https://osv.dev/vulnerability/CVE-2019-9517

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-9517/
Summaries are generated and may contain mistakes; the official description above is the record.