# CVE-2017-7783: Denial of service in Firefox

> An attacker can cause Firefox to hang or crash by using a long username in a site URL, resulting in a denial of service.

- **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:** 11 Jun 2018
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-ch5f-5368-9hw8, UBUNTU-CVE-2017-7783

## What is CVE-2017-7783?

CVE-2017-7783 is a high-severity denial of service vulnerability in Mozilla Firefox, published on 11 Jun 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

If a long user name is used in a username/password combination in a site URL (such as " http://UserName:Password@example.com"), the resulting modal prompt will hang in a non-responsive state or crash, causing a denial of service. This vulnerability affects Firefox < 55.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2017-7783?

It affects 1 product.


Products: Mozilla Firefox.

## How do I fix CVE-2017-7783?

Upgrade to a fixed version.

## Is CVE-2017-7783 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-7783 exists.

Public exploit code:

- Mozilla Firefox < 55 - Denial of Service (exploitdb)

## Other vulnerabilities in Mozilla Firefox

- [CVE-2019-11708](https://insights.sbomify.com/CVE-2019-11708/): Mozilla Firefox and Thunderbird Sandbox Escape (critical 10.0, exploited in the wild)
- [CVE-2010-3765](https://insights.sbomify.com/CVE-2010-3765/): Mozilla Multiple Products Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26486](https://insights.sbomify.com/CVE-2022-26486/): Mozilla Firefox Use-After-Free (critical 9.6, exploited in the wild)
- [CVE-2022-26485](https://insights.sbomify.com/CVE-2022-26485/): Mozilla Firefox Use-After-Free (high 8.8, exploited in the wild)
- [CVE-2019-11707](https://insights.sbomify.com/CVE-2019-11707/): Mozilla Firefox and Thunderbird Type Confusion (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-7783 and fix it if it is affected.

What it is: CVE-2017-7783 is a high-severity denial of service vulnerability in Mozilla Firefox, published on 11 Jun 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2017-7783 exists.

Affected product: Mozilla Firefox. 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-2017-7783/ (Markdown: https://insights.sbomify.com/CVE-2017-7783/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-7783
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-7783
- OSV: https://osv.dev/vulnerability/CVE-2017-7783

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-7783/
Summaries are generated and may contain mistakes; the official description above is the record.