# CVE-2016-3948: Denial of service in n/a

> Remote attackers can cause a denial of service in Squid proxy servers by sending crafted HTTP responses with malicious Vary headers.

- **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:** 7 Apr 2016
- **Updated:** 6 Aug 2024
- **Also known as:** DEBIAN-CVE-2016-3948, GHSA-f5f6-9f53-wf3r, UBUNTU-CVE-2016-3948

## What is CVE-2016-3948?

CVE-2016-3948 is a high-severity denial of service vulnerability in Squid-Cache Squid, published on 7 Apr 2016. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Squid 3.x before 3.5.16 and 4.x before 4.0.8 improperly perform bounds checking, which allows remote attackers to cause a denial of service via a crafted HTTP response, related to Vary headers.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2016-3948?

It affects 1 product.


Products: Squid-Cache Squid.

## How do I fix CVE-2016-3948?

Upgrade to a fixed version.

## Is CVE-2016-3948 being exploited?

There is no known exploitation of CVE-2016-3948 in the wild and no public exploit code.

## Other vulnerabilities in Squid-Cache Squid

- [CVE-2025-62168](https://insights.sbomify.com/CVE-2025-62168/): Squid vulnerable to information disclosure via authentication credential leakage in error handling (critical 10.0)
- [CVE-2025-54574](https://insights.sbomify.com/CVE-2025-54574/): Squid's URN Handling can lead to Buffer Overflow (critical 9.3)
- [CVE-2026-33526](https://insights.sbomify.com/CVE-2026-33526/): Squid vulnerable to Denial of Service in ICP Request handling (critical 9.2)
- [CVE-2026-32748](https://insights.sbomify.com/CVE-2026-32748/): Squid has Denial of Service in ICP Response handling (high 8.7)
- [CVE-2023-50269](https://insights.sbomify.com/CVE-2023-50269/): SQUID-2023:10 Denial of Service in HTTP Request parsing (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-3948 and fix it if it is affected.

What it is: CVE-2016-3948 is a high-severity denial of service vulnerability in Squid-Cache Squid, published on 7 Apr 2016. 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-2016-3948 in the wild and no public exploit code.

Affected product: Squid-Cache Squid. 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-2016-3948/ (Markdown: https://insights.sbomify.com/CVE-2016-3948/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-3948
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-3948
- OSV: https://osv.dev/vulnerability/CVE-2016-3948

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-3948/
Summaries are generated and may contain mistakes; the official description above is the record.