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Vulnerability · Published May 28, 2021 · Assigned by GitHub_M

CVE-2021-29492Bypass of path matching rules using escaped slash characters

High 8.1

In plain English

A high-severity path traversal in envoy from envoyproxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 63.1% (higher than 99.2% of all known vulnerabilities).

Severity (CVSS 3.1)8.1High
Exploit odds (30 days)63.1%top 0.8% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

VendorProductVersions
envoyproxy envoy <= 1.18.2

Weakness: CWE-22 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

References