CVE-2026-73548
HIGHDescription
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 forwards data for a configured non-WebSocket HTTP upgrade before the upstream accepts the upgrade. An unauthenticated HTTP/2 client can place a complete HTTP/1.1 request in extended CONNECT data; Envoy downgrades the request, writes the data unframed to a keep-alive HTTP/1.1 upstream, and returns the socket to the shared pool while the smuggled response remains queued. A different downstream client can then receive the attacker's response. The relevant scope boundary is that webSocket upgrades, plain CONNECT, disabled backend keep-alive, per-downstream pools, and max_requests_per_connection set to 1 are not affected by the demonstrated path. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Exploit Intelligence
Moderate risk: more likely to be exploited than 40% of all known CVEs.
References
Related Vulnerabilities
Other CWE-444 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-22536 | Critical | 10.0 | 98% | KEV | - |
| CVE-2025-61884 | High | 7.5 | 96% | KEV + Ransom | - |
| CVE-2020-9490 | High | 7.5 | 89% | - | Fix |
| CVE-2023-41265 | Critical | 9.6 | 88% | KEV + Ransom | - |
| CVE-2023-25690 | Critical | 9.8 | 85% | - | Fix |
| CVE-2022-32214 | Medium | 6.5 | 82% | - | Fix |
Common questions
How do I fix CVE-2026-73548?
Upgrade envoy to 1.39.1 or later.
Is CVE-2026-73548 being actively exploited?
Not that we know of. CVE-2026-73548 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.46% is the estimated probability that it will be exploited in the next 30 days. That is higher than 40% of all scored CVEs.
How severe is CVE-2026-73548?
CVE-2026-73548 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-73548 affect?
Published advisories record a fix for envoy (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-73548
Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-05.