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Authentication bypass in PyJWT versions prior to 2.13.0 allows remote attackers to forge valid JSON Web Tokens by exploiting an algorithm confusion flaw where the library fails to validate that a JSON Web Key intended for asymmetric verification is not reused as an HMAC shared secret. An attacker who knows the issuer's public key (typically distributed openly via JWKS endpoints) can sign HMAC-algorithm tokens with that public key and have them accepted as legitimate. No public exploit identified at time of analysis, though the underlying algorithm-confusion class is a well-documented JWT attack pattern.
Uncontrolled resource consumption in PyJWT 2.8.0-2.12.1 exposes any service that verifies detached JWS tokens to unauthenticated denial-of-service. When the unencoded-payload extension (b64=false, RFC 7797) is in use, PyJWT unnecessarily Base64URL-decodes the compact-serialization payload segment before discarding it in favor of the caller-supplied detached payload - turning that segment into an attacker-controlled amplifier for CPU and memory exhaustion regardless of signature validity. No public exploit has been identified at time of analysis, but the CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms fully unauthenticated remote exploitation against any affected endpoint using this feature.
Algorithm allow-list bypass in PyJWT 2.9.0-2.12.1 permits an attacker who controls a registered JWK/JWKS private key to circumvent caller-enforced algorithm restrictions during JWT signature verification. The library correctly checks the token header's alg claim against the caller-supplied allow-list, but then performs the actual cryptographic verification using the algorithm bound to the PyJWK object rather than the header-declared algorithm - creating a exploitable mismatch. Specifically, the documented PyJWKClient.get_signing_key_from_jwt() flow is affected, meaning applications relying on this pattern for algorithm-restricted JWT validation may accept tokens signed with algorithms they explicitly prohibited. No public exploit has been identified at time of analysis and the vulnerability is not listed in CISA KEV.
Unconstrained outbound JWKS requests in PyJWT's PyJWKClient.get_signing_key() allow unauthenticated remote attackers to amplify HTTP traffic toward a downstream JWKS endpoint by submitting JWTs carrying arbitrary, unrecognized kid values. All PyJWT versions prior to 2.13.0 are affected when the PyJWKClient class is used for signature verification. The availability impact is low (CVSS A:L) and exploitation success is gated on the upstream JWKS provider exhibiting rate limiting or transient failures; no public exploit code exists and this CVE does not appear in CISA KEV.
PyJWKClient in PyJWT prior to 2.13.0 passes attacker-influenced URIs directly to Python's urllib.request.urlopen() without restricting URI schemes, enabling Server-Side Request Forgery (SSRF) across file://, FTP, and data-URI schemes against applications that accept untrusted jku values. Affected deployments include any Python application using PyJWKClient where the jku URL originates from a JWT header, OAuth flow parameter, or externally influenced configuration. No public exploit exists and no CISA KEV listing is present; real-world exploitation is constrained by a CVSS-confirmed high attack complexity (AC:H) and required user interaction (UI:R), making opportunistic mass exploitation unlikely.
Authentication bypass in PyJWT versions prior to 2.13.0 allows remote attackers to forge valid JSON Web Tokens by exploiting an algorithm confusion flaw where the library fails to validate that a JSON Web Key intended for asymmetric verification is not reused as an HMAC shared secret. An attacker who knows the issuer's public key (typically distributed openly via JWKS endpoints) can sign HMAC-algorithm tokens with that public key and have them accepted as legitimate. No public exploit identified at time of analysis, though the underlying algorithm-confusion class is a well-documented JWT attack pattern.
Uncontrolled resource consumption in PyJWT 2.8.0-2.12.1 exposes any service that verifies detached JWS tokens to unauthenticated denial-of-service. When the unencoded-payload extension (b64=false, RFC 7797) is in use, PyJWT unnecessarily Base64URL-decodes the compact-serialization payload segment before discarding it in favor of the caller-supplied detached payload - turning that segment into an attacker-controlled amplifier for CPU and memory exhaustion regardless of signature validity. No public exploit has been identified at time of analysis, but the CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms fully unauthenticated remote exploitation against any affected endpoint using this feature.
Algorithm allow-list bypass in PyJWT 2.9.0-2.12.1 permits an attacker who controls a registered JWK/JWKS private key to circumvent caller-enforced algorithm restrictions during JWT signature verification. The library correctly checks the token header's alg claim against the caller-supplied allow-list, but then performs the actual cryptographic verification using the algorithm bound to the PyJWK object rather than the header-declared algorithm - creating a exploitable mismatch. Specifically, the documented PyJWKClient.get_signing_key_from_jwt() flow is affected, meaning applications relying on this pattern for algorithm-restricted JWT validation may accept tokens signed with algorithms they explicitly prohibited. No public exploit has been identified at time of analysis and the vulnerability is not listed in CISA KEV.
Unconstrained outbound JWKS requests in PyJWT's PyJWKClient.get_signing_key() allow unauthenticated remote attackers to amplify HTTP traffic toward a downstream JWKS endpoint by submitting JWTs carrying arbitrary, unrecognized kid values. All PyJWT versions prior to 2.13.0 are affected when the PyJWKClient class is used for signature verification. The availability impact is low (CVSS A:L) and exploitation success is gated on the upstream JWKS provider exhibiting rate limiting or transient failures; no public exploit code exists and this CVE does not appear in CISA KEV.
PyJWKClient in PyJWT prior to 2.13.0 passes attacker-influenced URIs directly to Python's urllib.request.urlopen() without restricting URI schemes, enabling Server-Side Request Forgery (SSRF) across file://, FTP, and data-URI schemes against applications that accept untrusted jku values. Affected deployments include any Python application using PyJWKClient where the jku URL originates from a JWT header, OAuth flow parameter, or externally influenced configuration. No public exploit exists and no CISA KEV listing is present; real-world exploitation is constrained by a CVSS-confirmed high attack complexity (AC:H) and required user interaction (UI:R), making opportunistic mass exploitation unlikely.