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Fencer Vulns
medium 5.4

CVE-2023-27491 json

Envoy forwards invalid Http2/Http3 downstream headers

published 2023-04-04 3 y ago modified 2026-09-08 2 mo ago also BIT-envoy-2023-27491 , EUVD-2023-31256 , GHSA-5jmv-cw9p-f9rp

cvss
5.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 59%
public exploits
0
none known

Summary

Envoy is an open source edge and service proxy designed for cloud-native applications. Compliant HTTP/1 service should reject malformed request lines. Prior to versions 1.26.0, 1.25.3, 1.24.4, 1.23.6, and 1.22.9, There is a possibility that non compliant HTTP/1 service may allow malformed requests, potentially leading to a bypass of security policies. This issue is fixed in versions 1.26.0, 1.25.3, 1.24.4, 1.23.6, and 1.22.9.

Patch / fix

  • bitnami envoy 1.22.9, 1.23.6, 1.24.4, 1.25.3
  • envoyproxy envoy 1.22.9, 1.23.6, 1.24.4, 1.25.3

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-27491 updated cvss 6.5

envoy: Envoy forwards invalid HTTP/2 and HTTP/3 downstream

  • Red Hat OpenShift Service Mesh 2.1 servicemesh-proxy, servicemesh-proxy-wasm
    affected: no fix planned “Will not fix”
  • Red Hat RHOSSM 2.2 for RHEL 8 openshift-service-mesh/proxyv2-rhel8 2.2.9-2
    fixed: vendor fix RHSA-2023:4623
  • Red Hat RHOSSM 2.2 for RHEL 8 openshift-service-mesh/pilot-rhel8 2.2.9-1, openshift-service-mesh/grafana-rhel8 2.2.9-1, openshift-service-mesh/istio-cni-rhel8 2.2.9-1, openshift-service-mesh/ratelimit-rhel8 2.2.9-1, openshift-service-mesh/prometheus-rhel8 2.2.9-1, openshift-service-mesh/istio-must-gather-rhel8 2.2.9-2
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
20 mo ago

Exploit prediction

0.88% chance of exploitation in the next 30 days, higher than 59% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/envoyproxy/envoy/security/advisories/GHSA-5jmv-cw9p-f9rp referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
NVD 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
OSV 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
bitnami envoy
<1.22.9
>=1.23.0, <1.23.6
>=1.24.0, <1.24.4
>=1.25.0, <1.25.3
1.22.9
1.23.6
1.24.4
1.25.3

Affected products

  • envoyproxy envoy

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.