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Fencer Vulns
high 8.1

CVE-2021-29492 in the critical feed json

Bypass of path matching rules using escaped slash characters

published 2021-05-28 5 y ago modified 2026-09-08 2 mo ago also BIT-envoy-2021-29492 , EUVD-2021-16089 , GHSA-4987-27fx-x6cf

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
63.1%
EPSS 63.1% chance of exploitation in 30 days, percentile 99.2%
public exploits
0
none known

Summary

Envoy is a cloud-native edge/middle/service proxy. Envoy does not decode escaped slash sequences `%2F` and `%5C` in HTTP URL paths in versions 1.18.2 and before. A remote attacker may craft a path with escaped slashes, e.g. `/something%2F..%2Fadmin`, to bypass access control, e.g. a block on `/admin`. A backend server could then decode slash sequences and normalize path and provide an attacker access beyond the scope provided for by the access control policy. ### Impact Escalation of Privileges when using RBAC or JWT filters with enforcement based on URL path. Users with back end servers that interpret `%2F` and `/` and `%5C` and `\` interchangeably are impacted. ### Attack Vector URL paths containing escaped slash characters delivered by untrusted client. Patches in versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. As a workaround, if back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, one may reconfigure the back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably.

Patch / fix

  • bitnami envoy 1.15.5, 1.16.4, 1.17.3, 1.18.3
  • envoyproxy envoy 1.15.5, 1.16.4, 1.17.3, 1.18.3
  • servicemesh service mesh 2.0 2.0.4-1.el8
  • servicemesh-mixc service mesh 2.0 2.0.4-1.el8
  • servicemesh-mixs service mesh 2.0 2.0.4-1.el8
  • servicemesh-proxy service mesh 2.0 2.0.4-1.el8
  • servicemesh-istioctl service mesh 2.0 2.0.4-1.el8
  • servicemesh-operator service mesh 2.0 2.0.4-3.el8
  • servicemesh-pilot-agent service mesh 2.0 2.0.4-1.el8
  • servicemesh-pilot-discovery service mesh 2.0 2.0.4-1.el8

red hat advisories RHSA-2021:1538RHSA-2021:1540

  • istio Arch Linux 1.10.0-1

arch linux advisories AVG-1947

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-2021-29492 updated cvss 8.3

envoyproxy/envoy: HTTP request with escaped slash characters can bypass Envoy's authorization mechanisms

  • Red Hat OpenShift Service Mesh 1.1 servicemesh-proxy 1.1.14-1.el8
    fixed: vendor fix RHSA-2021:1540
  • Red Hat OpenShift Service Mesh 2.0 servicemesh-proxy 2.0.4-1.el8, servicemesh-operator 2.0.4-3.el8
    fixed: vendor fix RHSA-2021:1538
  • Red Hat OpenShift Service Mesh 1.1 servicemesh 1.1.14-1.el8, servicemesh-mixc 1.1.14-1.el8, servicemesh-mixs 1.1.14-1.el8, servicemesh-galley 1.1.14-1.el8, servicemesh-citadel 1.1.14-1.el8, servicemesh-istioctl 1.1.14-1.el8, +3 more Red Hat OpenShift Service Mesh 2.0 servicemesh 2.0.4-1.el8, servicemesh-mixc 2.0.4-1.el8, servicemesh-mixs 2.0.4-1.el8, servicemesh-istioctl 2.0.4-1.el8, servicemesh-pilot-agent 2.0.4-1.el8, servicemesh-pilot-discovery 2.0.4-1.el8
    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

Exploit prediction

63.10% chance of exploitation in the next 30 days, higher than 99.2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
OSV 3.1 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

Affected packages

ecosystem package affected fixed in
bitnami envoy
<1.15.5
>=1.16.0, <1.16.4
>=1.17.0, <1.17.3
>=1.18.0, <1.18.3
1.15.5
1.16.4
1.17.3
1.18.3

Affected products

  • envoyproxy envoy

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory

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.