CVE-2026-48521: Envoy is an open source edge and service proxy designed for cloud-native applications

This week

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-48521 is a medium-severity flaw (CVSS 5.9) affecting envoy. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transport_socket_options while selecting an HTTP/3 connection pool without first checking whether the pointer is null. LoadBalancerContext implementations used by synthetic, mirror, health-check, and async-client calls can return no transport-socket op

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
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-476
Published	2026-09-21
Last modified	2026-10-05

Publisher (CNA): GitHub, Inc. · Vendor: envoyproxy

Last updated 2026-10-05 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-21 20:17 UTCPublished CVE record published
2026-10-05 14:09 UTCUpdated Record last modified

envoyproxy envoy UPGRADE

Affected: < 1.36.10 · >= 1.37.0 and < 1.37.6 · >= 1.38.0 and < 1.38.4 · >= 1.39.0 and < 1.39.1

Fixed in: 1.36.10, 1.37.6, 1.38.4, 1.39.1

Safe to downgrade to: a release before 1.37.0

1. Check installed version

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

2. UPGRADE to 1.36.10 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade envoy

Note

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

3. If no update is available yet, DOWNGRADE to a release before 1.37.0 (Debian / Ubuntu)

apt-cache madison envoy sudo apt install envoy=<VERSION_BEFORE_1.37.0> sudo apt-mark hold envoy

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list envoy sudo dnf downgrade envoy-<VERSION_BEFORE_1.37.0> sudo dnf versionlock add envoy

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Advisories and coverage

Official advisories

Google Cloud Security Bulletins: GCP-2026-057 2026-10-26
Amazon Linux 2 ALAS: ALAS2ECS-2026-137 (important): ecs-service-connect-agent 2026-09-14

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-2026-48521?

envoy: upgrade to 1.36.10, 1.37.6, 1.38.4, 1.39.1. Exact commands for each OS are on this page.

Is CVE-2026-48521 being exploited?

CVE-2026-48521 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-2026-48521 affect?

CVE-2026-48521 affects envoy. Severity is medium (CVSS 5.9). Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's ProdClusterManagerFactory::allocateConnPool dereferences transport_socket_options while selecting a

How urgent is CVE-2026-48521?

Priority 44/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Envoy vulnerabilities

Related CVEs

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References

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