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CVE-2021-21378
CVE ID
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CVE-2021-21378
MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
Discovery
Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
Topic Tags
Description
Envoy is a cloud-native high-performance edge/middle/service proxy. In Envoy version 1.17.0 an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list when Envoy’s JWT Authentication filter is configured with the allow_missing requirement under requires_any due to a mistake in implementation. Envoy’s JWT Authentication filter can be configured with the allow_missing requirement that will be satisfied if JWT is missing (JwtMissed error) and fail if JWT is presented or invalid. Due to a mistake in implementation, a JwtUnknownIssuer error was mistakenly converted to JwtMissed when requires_any was configured. So if allow_missing was configured under requires_any, an attacker can bypass authentication by presenting a JWT token with an issuer that is not in the provider list. Integrity may be impacted depending on configuration if the JWT token is used to protect against writes or modifications. This regression was introduced on 2020/11/12 in PR 13839 which fixed handling allow_missing under RequiresAny in a JwtRequirement (see issue 13458). The AnyVerifier aggregates the children verifiers’ results into a final status where JwtMissing is the default error. However, a JwtUnknownIssuer was mistakenly treated the same as a JwtMissing error and the resulting final aggregation was the default JwtMissing. As a result, allow_missing would allow a JWT token with an unknown issuer status. This is fixed in version 1.17.1 by PR 15194. The fix works by preferring JwtUnknownIssuer over a JwtMissing error, fixing the accidental conversion and bypass with allow_missing. A user could detect whether a bypass occurred if they have Envoy logs enabled with debug verbosity. Users can enable component level debug logs for JWT. The JWT filter logs will indicate that there is a request with a JWT token and a failure that the JWT token is missing.
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CVSS V3 Severity and Metrics
General Information
Vendors
- envoyproxy
Products
- envoy 1.17.0
References
Additional Info
Technical Analysis
Report as Emergent Threat Response
Report as Exploited in the Wild
CVE ID
AttackerKB requires a CVE ID in order to pull vulnerability data and references from the CVE list and the National Vulnerability Database. If available, please supply below:
