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CVE-2021-29492

Bypass of path matching rules using escaped slash characters

CVSS 3.1 High 8.1

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Description

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.

Official description from the CVE record, published by GitHub_M. Copyright © 1999-2026 The MITRE Corporation. See /security/cve/legal for the CVE license. View the record on cve.org

Key data

CVSS 3.1 High 8.1

Score published by GitHub_M in the CVE record.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

  • Attack vector: Network

    The vulnerable component can be reached over a network, possibly from the Internet.

  • Attack complexity: High

    The attack depends on conditions outside the attacker's control, so it takes preparation.

  • Privileges required: None

    No account or privileges are needed.

  • User interaction: None

    No action from any user is needed.

  • Scope: Unchanged

    The impact stays within the vulnerable component.

  • Confidentiality impact: High

    Serious or total effect on the secrecy of data.

  • Integrity impact: High

    Serious or total effect on the trustworthiness of data.

  • Availability impact: High

    Serious or total effect on availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.
Score
0.63096 (63.1% probability)
Percentile
99.2%
Scores of
Nov 10, 2026
Model
v2026.06.15

Weakness (CWE)

CWE catalog version 5.0.
CWE names: Copyright © 2006-2026, The MITRE Corporation. See /security/cve/legal for the CWE license.
  • CWE-22Improper Limitation of a Pathname to a Restricted Directory

Affected products

Products listed in the CVE record, as the CNA published them.

  • envoyproxy envoy

    • affected: <= 1.18.2

References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

Timeline

  1. ID reserved
  2. Record published
  3. Record last updated

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About CubePath

CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection.
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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:53 UTC. Sources and licenses