CVE-2026-35191: Issue summary: The OpenSSL QUIC server, when configured to not preform address validation, can be forced to co

Q: How do I fix CVE-2026-35191?

openssl: upgrade to 3.5.9, 3.6.5, 4.0.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-35191 being exploited?

CVE-2026-35191 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-35191 affect?

CVE-2026-35191 affects openssl. Severity is low (CVSS 3.7). 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 conn

Q: How urgent is CVE-2026-35191?

Priority 36/100. Remotely exploitable, no login, no user action; On your watchlist

Routine

LOW 3.7REMOTEWATCHLISTUPGRADE

CVE-2026-35191 is a low-severity flaw (CVSS 3.7) affecting openssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 amplific

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-440
Published	2026-09-29
Last modified	2026-10-08

Publisher (CNA): OpenSSL Software Foundation · Vendor: openssl

Last updated 2026-10-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-29 16:17 UTCPublished CVE record published
2026-10-08 01:02 UTCUpdated Record last modified

openssl openssl UPGRADE

Affected: >= 3.5.0 and < 3.5.9 · >= 3.6.0 and < 3.6.5 · >= 4.0.0 and < 4.0.3

Fixed in: 3.5.9, 3.6.5, 4.0.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy openssl || rpm -q openssl || openssl --version

2. UPGRADE to 3.5.9 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade openssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade openssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3204 (important): openssl 2026-10-12
OpenSSL Vulnerabilities: OpenSSL 4.0.3 2026-09-29
OpenSSL Vulnerabilities: OpenSSL 3.6.5 2026-09-29
OpenSSL Vulnerabilities: OpenSSL 3.5.9 2026-09-29

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-35191?

openssl: upgrade to 3.5.9, 3.6.5, 4.0.3. Exact commands for each OS are on this page.

Is CVE-2026-35191 being exploited?

CVE-2026-35191 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-35191 affect?

CVE-2026-35191 affects openssl. Severity is low (CVSS 3.7). 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 conn

How urgent is CVE-2026-35191?

Priority 36/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

OpenSSL vulnerabilities

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References

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