Vulnerability Details : CVE-2021-29492
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.
Vulnerability category: Directory traversal
Products affected by CVE-2021-29492
- cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
- cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
- cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
- cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
Exploit prediction scoring system (EPSS) score for CVE-2021-29492
0.27%
Probability of exploitation activity in the next 30 days
EPSS Score History
~ 67 %
Percentile, the proportion of vulnerabilities that are scored at or less
CVSS scores for CVE-2021-29492
| Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source | First Seen |
|---|---|---|---|---|---|---|
|
7.5
|
HIGH | AV:N/AC:L/Au:N/C:P/I:P/A:P |
10.0
|
6.4
|
NIST | |
|
8.3
|
HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L |
3.9
|
3.7
|
NIST | |
|
8.1
|
HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
2.2
|
5.9
|
GitHub, Inc. |
CWE ids for CVE-2021-29492
-
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.Assigned by: security-advisories@github.com (Primary)
References for CVE-2021-29492
-
https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf
Bypass of path matching rules using escaped slash characters · Advisory · envoyproxy/envoy · GitHubMitigation;Third Party Advisory
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