# CVE-2026-66257: Apache Qpid Proton-J: Unbounded symbol value caching can lead to pre-authentication resource exhaustion

> A pre-authentication attacker can cause resource exhaustion and denial of service via unbounded symbol value caching in Apache Qpid Proton-J.

- **Severity:** High 7.5 (`CVSS:3.1/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:** 5 Aug 2026
- **Updated:** 6 Aug 2026
- **Also known as:** CLEANSTART-2026-KJ02957, GHSA-g4xc-w2cq-f2f8

## What is CVE-2026-66257?

CVE-2026-66257 is a high-severity denial of service vulnerability in Apache Qpid Proton-J, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A pre-authentication attacker could leverage unbounded symbol value caching to cause resource exhaustion leading to denial of service.

This issue affects Apache Qpid Proton-J: through 0.34.1.

Users are recommended to upgrade to version 0.35.0, which fixes the issue.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-66257?

It affects 1 product.


Products: Apache Qpid Proton-J.

## How do I fix CVE-2026-66257?

Upgrade to a fixed version.

## Is CVE-2026-66257 being exploited?

There is no known exploitation of CVE-2026-66257 in the wild and no public exploit code.

## Other vulnerabilities in Apache Qpid Proton-J

- [CVE-2026-66273](https://insights.sbomify.com/CVE-2026-66273/): Apache Qpid Proton-J: Type size/count handling can lead to excessive allocation pre-authentication (high 7.5)
- [CVE-2026-66274](https://insights.sbomify.com/CVE-2026-66274/): Apache Qpid Proton-J: Unbounded type nesting can lead to pre-authentication stackoverflow (high 7.5)
- [CVE-2018-17187](https://insights.sbomify.com/CVE-2018-17187/): Improper Certificate Validation in proton-j (high 7.4)
- [CVE-2026-66275](https://insights.sbomify.com/CVE-2026-66275/): Apache Qpid Proton-J: Incoming session flow control window can be exceeded (medium 6.5)
- [CVE-2026-66276](https://insights.sbomify.com/CVE-2026-66276/): Apache Qpid Proton-J: Unbounded disposition range handling can lead to denial of service (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66257 and fix it if it is affected.

What it is: CVE-2026-66257 is a high-severity denial of service vulnerability in Apache Qpid Proton-J, published on 5 Aug 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-2026-66257 in the wild and no public exploit code.

Affected product: Apache Qpid Proton-J. 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-2026-66257/ (Markdown: https://insights.sbomify.com/CVE-2026-66257/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66257
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66257
- OSV: https://osv.dev/vulnerability/CVE-2026-66257

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-66257/
Summaries are generated and may contain mistakes; the official description above is the record.