# CVE-2026-35191: QUIC Unvalidated Amplification Credit may be Over Accounted

> Remote attackers can exploit a logic error in OpenSSL's QUIC server to bypass amplification limits, enabling DDoS attacks when address validation is disabled.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Sep 2026
- **Updated:** 30 Sep 2026
- **Also known as:** AZL-105462, AZL-105531, AZL-105612, AZL-105837, AZL-105885, BELL-CVE-2026-35191, CLEANSTART-2026-SP65833, DEBIAN-CVE-2026-35191, GHSA-5p85-47cf-3663, MINI-qj26-vxc4-g9r9, UBUNTU-CVE-2026-35191

## What is CVE-2026-35191?

CVE-2026-35191 is a low-severity denial of service vulnerability in Openssl Openssl, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Issue summary: The OpenSSL QUIC server, when configured to not preform address
validation, can be forced to count incoming packets multiple times in its
unvalidated credit computation, leading to a violation of the RFC 9000
unvalidated connection amplification limit of 3 times the amount of data
received.

Impact summary: A remote attacker able to spoof packets to a server using the
OpenSSL QUIC implementation might use the server for an amplification of
a DDoS attack.

CWE: CWE-440: Expected Behavior Violation 

Description: OpenSSL's QUIC stack, when operating as a server, enforces client
address validation (RFC 9000, Section 8), to confirm the peer address is not
used for a traffic amplification attack.  If this feature is disabled on the
server, the QUIC stack limits the amount of server data that can be sent to 3
times the amount of data received from the peer address, until such time as the
TLS handshake is completed.

The OpenSSL QUIC server, when operating in non-validation mode, adds the
length of the whole datagram received to the unvalidated credit limit when
processing each QUIC packet in the datagram. A remote peer may,
after establishing a connection with an initial client hello frame, send a
subsequent datagram containing multiple QUIC packets, leading the server to
account the entire datagram length for each packet in the datagram, resulting
in the server believing that the peer has sent more data than it actually has,
thereby violating the 3x amplification limit mandated by the RFC.

FIPS impact: no
As the QUIC stack lives outside the FIPS module boundary, no FIPS modules
are affected by this CVE.

Weakness: CWE-440 (Expected Behavior Violation)

## Which versions are affected by CVE-2026-35191?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-35191?

Apply the vendor's patch.

## Is CVE-2026-35191 being exploited?

There is no known exploitation of CVE-2026-35191 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-35191 and fix it if it is affected.

What it is: CVE-2026-35191 is a low-severity denial of service vulnerability in Openssl Openssl, published on 29 Sep 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-2026-35191 in the wild and no public exploit code.

Affected product: Openssl Openssl. 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-2026-35191/ (Markdown: https://insights.sbomify.com/CVE-2026-35191/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-35191
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-35191
- OSV: https://osv.dev/vulnerability/CVE-2026-35191

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-35191/
Summaries are generated and may contain mistakes; the official description above is the record.