CVE-2021-29492
"Envoy URL Path Escalation Vulnerability"
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.
INFO
Published Date :
May 28, 2021, 9:15 p.m.
Last Modified :
Nov. 21, 2024, 6:01 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 2.0 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update the affected Envoy packages to a non-vulnerable version.
- If using a backend server that interprets `%2F` and `/` and `%5C` and `\` interchangeably, reconfigure the server to not treat them interchangeably.
Public PoC/Exploit Available at Github
CVE-2021-29492 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2021-29492.
| URL | Resource |
|---|---|
| https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf | Mitigation Third Party Advisory |
| https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf | Mitigation Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2021-29492 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2021-29492
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Official Ambassador API Gateway Documentation repository
api-gateway kubernetes docker envoyproxy
Makefile Python JavaScript TypeScript Less Shell CSS
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2021-29492 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2021-29492 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Nov. 21, 2024
Action Type Old Value New Value Added Reference https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf -
CVE Modified by [email protected]
May. 14, 2024
Action Type Old Value New Value -
Reanalysis by [email protected]
Dec. 10, 2021
Action Type Old Value New Value Removed CVSS V3.1 NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CVSS V3.1 NIST AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L -
Initial Analysis by [email protected]
Jun. 10, 2021
Action Type Old Value New Value Added CVSS V2 NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P) Added CVSS V3.1 NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Changed Reference Type https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf No Types Assigned https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cf Mitigation, Third Party Advisory Added CPE Configuration OR *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions up to (excluding) 1.15.5 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.16.0 up to (excluding) 1.16.4 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.17.0 up to (excluding) 1.17.3 *cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* versions from (including) 1.18.0 up to (excluding) 1.18.3 -
CVE Modified by [email protected]
Jun. 07, 2021
Action Type Old Value New Value Changed Description ### Description 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 Envoy versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. ### Workarounds If back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, we recommend reconfiguring back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably if feasible. ### Credit Ruilin Yang ([email protected]) ### References https://blog.envoyproxy.io https://github.com/envoyproxy/envoy/releases ### For more information If you have any questions or comments about this advisory: * Open an issue in [Envoy repo](https://github.com/envoyproxy/envoy/issues) * Email us at [envoy-security](mailto:[email protected]) 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. -
CVE Modified by [email protected]
May. 28, 2021
Action Type Old Value New Value Changed Description ### Description 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 Envoy versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. ### Workarounds If back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, we recommend reconfiguring back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably if feasible. ### Credit Ruilin Yang ([email protected]) ### References https://blog.envoyproxy.io https://github.com/envoyproxy/envoy/releases ### For more information If you have any questions or comments about this advisory: * Open an issue in [Envoy repo](https://github.com/envoyproxy/envoy/issues) * Email us at [envoy-security](mailto:[email protected]) ### Description 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 Envoy versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. ### Workarounds If back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, we recommend reconfiguring back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably if feasible. ### Credit Ruilin Yang ([email protected]) ### References https://blog.envoyproxy.io https://github.com/envoyproxy/envoy/releases ### For more information If you have any questions or comments about this advisory: * Open an issue in [Envoy repo](https://github.com/envoyproxy/envoy/issues) * Email us at [envoy-security](mailto:[email protected])
Vulnerability Scoring Details
Base CVSS Score: 8.3
Base CVSS Score: 7.5
Exploit Prediction
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days.
7.42 }} -6.60%
score
0.90892
percentile