CVE-2026-73550: Envoy is an open source edge and service proxy designed for cloud-native applications

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HIGH 7.5REMOTEUPGRADE

CVE-2026-73550 is a high-severity flaw (CVSS 7.5) 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 copies every decoded HTTP/2 Host header value before discarding it when :authority is already present. The discarded value bypasses saveHeader, so its bytes and count are not charged against request header limits. An unauthenticated client can use HPACK indexing to submit many references to a large Host value

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-401
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 14:07 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.

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-2026-73550?

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-2026-73550 being exploited?

CVE-2026-73550 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-2026-73550 affect?

CVE-2026-73550 affects envoy. Severity is high (CVSS 7.5). 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 copies every decoded HTTP/2 Host header value before discarding it when :authority is already present

How urgent is CVE-2026-73550?

Priority 48/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Envoy vulnerabilities

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References

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