# CVE-2026-75804: QUIC Connection-Level Flow Control is Not Enforced for Streams

> A remote attacker can cause excessive memory allocation in the OpenSSL QUIC stack by bypassing connection-level flow control, leading to denial of service.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/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:** 29 Sep 2026
- **Also known as:** ALPINE-CVE-2026-75804, AZL-105458, AZL-105510, AZL-105594, AZL-105636, AZL-105855, AZL-105894, BELL-CVE-2026-75804, CLEANSTART-2026-DS32463, DEBIAN-CVE-2026-75804, GHSA-gjmh-wx93-r4pw, MINI-9j77-6wjw-8vwx, UBUNTU-CVE-2026-75804

## What is CVE-2026-75804?

CVE-2026-75804 is a medium-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: OpenSSL QUIC stack does not enforce connection
level flow control for streams. Remote peers may send more bytes
as long as they fit within the stream flow control limits.

Impact summary: A malicious remote peer may exploit the lack of connection
flow control for streams to make the QUIC stack receive ~100MB of memory
instead of 768 KiB (default flow control window size).

CWE: CWE-770: Allocation of Resources Without Limits or Throttling

Description: The local QUIC stack advertises two flow control limits
to its remote peer: stream flow control limit and connection flow
control limit. The remote peer must follow both limits when transmitting
stream data.

Whenever the local QUIC stack receives a stream frame, it validates
that the size of the received stream frame stays within flow control limits.
If either limit is exceeded (stream level or connection level), then
the QUIC stack must close the connection with a flow control error.

The vulnerable OpenSSL QUIC stack enforces the stream-level but not
the connection-level limit. To exploit the issue, three conditions must be met:
  - the remote peer opens several streams
  - each stream must stay within the stream-level flow control limit
  - there must be no zero-offset byte sent on any of the streams
    (to prevent the vulnerable QUIC stack from consuming data).
By meeting the conditions above, the remote peer may make the local stack
allocate 2 x MAX_STREAMS x (stream flow control limit) bytes
of memory. MAX_STREAMS defaults to 100, and the limit applies to both
bidirectional and unidirectional streams, making it 200 in total. The default
flow control window for a stream is 512kB. The remote peer may
force the vulnerable QUIC stack to allocate 100MB of heap per connection.

FIPS impact: no
The FIPS module is not affected as the QUIC implementation is outside of
the OpenSSL FIPS module boundary.

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

## Which versions are affected by CVE-2026-75804?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-75804?

Apply the vendor's patch.

## Is CVE-2026-75804 being exploited?

There is no known exploitation of CVE-2026-75804 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-2026-75804 and fix it if it is affected.

What it is: CVE-2026-75804 is a medium-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-2026-75804 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-2026-75804/ (Markdown: https://insights.sbomify.com/CVE-2026-75804/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-75804
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-75804
- OSV: https://osv.dev/vulnerability/CVE-2026-75804

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-75804/
Summaries are generated and may contain mistakes; the official description above is the record.