CVE-2026-102269

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.

Summary

PyJWT 2.13.0 accepts compact JWS signature segments containing characters that are not in the Base64URL alphabet. Appending !!!! to a valid signature does not change the decoded signature bytes or authenticated claims, but it changes the serialized token and its SHA-256 hash. An application that indexes logout or revocation state by the raw token therefore rejects the logged-out token and accepts its no-key alternate serialization.

This report separates two issues: permissive compact-JWS decoding is the library behavior, while using raw serialized JWT text as a security identity is a dangerous application composition. A jti-indexed control blocks both representations.

Affected Version

Confirmed with PyJWT 2.13.0 on CPython 3.13. The mutation changes only the signature segment and requires no signing key.

End-to-End Reproduction

.venv-research/bin/python 06-practical-testing/revocation-bypass-lab.py

The loopback-only lab performs:

1. Issue a valid HS256 admin token.
2. Access /protected successfully.
3. Log out the canonical token and store SHA256(raw_token).
4. Confirm canonical replay returns HTTP 401.
5. Append !!!! to only the signature segment.
6. Confirm the mutated token has the same verified claims and signature bytes, a different raw hash, and receives HTTP 200.
7. Repeat with jti-indexed revocation and confirm both forms return HTTP 401.

Observed statuses for raw-token revocation were 200 -> logout -> 401 for the canonical token and 200 for the alternate serialization. The jti control returned 401 for both replays after logout.

Security Boundaries and Severity

This is not signature forgery: the attacker starts with a valid token and cannot alter its claims. Impact requires a consumer to bind revocation, replay state, rate limits, or cache identity to the raw compact string. Under that composition, an authenticated user can bypass logout or token-specific revocation without the signing key. Medium is suggested for triage because the security impact is real but application-dependent.

Recommended Fix

• Reject signature segments containing characters outside [A-Za-z0-9_-].
• Reject padding and other non-canonical Base64URL encodings for compact JWS.
• Add regression tests proving malformed signature encodings fail before or during verification.
• Document that applications must use a semantic identifier such as jti, not the raw serialized token, for revocation and replay state.

Maintainer update — 2026-09-09

We reproduced the reported behavior on the verified master commit 8915570: appending !!!! to a valid compact-JWS signature segment is accepted, produces the same decoded signature bytes and claims, and changes the serialized token hash. Existing JWS verification controls pass. The behavior is present in the tested release range represented by tags 2.4.0, 2.8.0, 2.10.1, 2.12.1, and 2.13.0.

The security impact is conditional on an application using the raw serialized token as the identity for logout, revocation, replay, rate-limit, or cache state. Under that composition, an attacker who already holds a valid token can use an alternate serialization after the canonical string is revoked. This is not signature forgery or claim alteration; applications should use a semantic identifier such as jti for token identity.

The report is ready to be accepted as a draft for continued remediation. A narrow fix assessment recommends rejecting non-canonical Base64URL characters and padding in compact-JWS segments. No fix commit or release is claimed yet.

Maintainer update — 2026-09-09

The fix has been rebased onto the current master as e6f48401001609a8f99e71fcaf355fb895d508a8 and is ready to be pushed. Compact-JWS header, payload, and signature segments are now required to use the unpadded Base64URL alphabet and canonical re-encoding; a signature segment containing non-canonical characters such as !!!! is rejected…

setup.py test %endif

Security Fix(es):

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT get_signing_key_from_jwt is affected because unknown kid misses force refreshes without a negative cache or minimum refresh interval. This occurs when unauthenticated tokens repeatedly use the same unknown kid or varying kid values absent from the cached JWKS. As a result, each cache miss causes PyJWKClient to refresh the JWKS. Consequently, attacker traffic can amplify outbound requests to the configured JWKS endpoint. This issue is fixed in version 2.14.0.(CVE-2026-101917)

PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.(CVE-2026-101918)

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.(CVE-2026-102265)

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.(CVE-2026-102269)

PyJWT is a Python implementation of JSON Web Token standards. From 2.1.0 until 2.15.0, PyJWT OKPAlgorithm.from_jwk in jwt/algorithms.py is affected because private-JWK import path does not compare the public key derived from d with x. This occurs when an OKP private JWK supplies non-corresponding x and d components. As a result, identity derived from x can differ from operations performed with d. Consequently, if an integration also accepts private key parameters from a proof header without rejecting them, an attacker may use a stolen sender-constrained token without the legitimate private key. This issue is fixed in version 2.15.0.(CVE-2026-102275)

setup.py test %endif

Security Fix(es):

PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.(CVE-2026-101918)

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.(CVE-2026-102265)

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.(CVE-2026-102269)

PyJWT is a Python implementation of JSON Web Token standards. From 2.1.0 until 2.15.0, PyJWT OKPAlgorithm.from_jwk in jwt/algorithms.py is affected because private-JWK import path does not compare the public key derived from d with x. This occurs when an OKP private JWK supplies non-corresponding x and d components. As a result, identity derived from x can differ from operations performed with d. Consequently, if an integration also accepts private key parameters from a proof header without rejecting them, an attacker may use a stolen sender-constrained token without the legitimate private key. This issue is fixed in version 2.15.0.(CVE-2026-102275)

setup.py test %endif

Security Fix(es):

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT get_signing_key_from_jwt is affected because unknown kid misses force refreshes without a negative cache or minimum refresh interval. This occurs when unauthenticated tokens repeatedly use the same unknown kid or varying kid values absent from the cached JWKS. As a result, each cache miss causes PyJWKClient to refresh the JWKS. Consequently, attacker traffic can amplify outbound requests to the configured JWKS endpoint. This issue is fixed in version 2.14.0.(CVE-2026-101917)

PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.(CVE-2026-101918)

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.(CVE-2026-102265)

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.(CVE-2026-102269)

PyJWT is a Python implementation of JSON Web Token standards. From 2.1.0 until 2.15.0, PyJWT OKPAlgorithm.from_jwk in jwt/algorithms.py is affected because private-JWK import path does not compare the public key derived from d with x. This occurs when an OKP private JWK supplies non-corresponding x and d components. As a result, identity derived from x can differ from operations performed with d. Consequently, if an integration also accepts private key parameters from a proof header without rejecting them, an attacker may use a stolen sender-constrained token without the legitimate private key. This issue is fixed in version 2.15.0.(CVE-2026-102275)

setup.py test %endif

Security Fix(es):

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT get_signing_key_from_jwt is affected because unknown kid misses force refreshes without a negative cache or minimum refresh interval. This occurs when unauthenticated tokens repeatedly use the same unknown kid or varying kid values absent from the cached JWKS. As a result, each cache miss causes PyJWKClient to refresh the JWKS. Consequently, attacker traffic can amplify outbound requests to the configured JWKS endpoint. This issue is fixed in version 2.14.0.(CVE-2026-101917)

PyJWT is a Python implementation of JSON Web Token standards. From 2.0.0a1 until 2.15.0, PyJWT PyJWKClient.get_signing_key_from_jwt is affected because payload parser catches ValueError but not RecursionError. This occurs when an attacker-controlled recursively nested payload reaches json.loads. As a result, documented PyJWT exception handling does not contain the failure. Consequently, an unauthenticated request can raise an exception that may produce an HTTP 500 response. The advisory-defined affected implementation also includes jwt/api_jwt.py, verify_signature=False. This issue is fixed in version 2.15.0.(CVE-2026-101918)

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, PyJWS._load in jwt/api_jws.py is affected because parser catches ValueError but not RecursionError. This occurs when a deeply nested token header reaches json.loads. As a result, RecursionError escapes the documented PyJWT error hierarchy. Consequently, an unauthenticated malformed token can cause a request-level failure and HTTP 500. This issue is fixed in version 2.14.0.(CVE-2026-102265)

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.(CVE-2026-102269)

PyJWT is a Python implementation of JSON Web Token standards. From 2.1.0 until 2.15.0, PyJWT OKPAlgorithm.from_jwk in jwt/algorithms.py is affected because private-JWK import path does not compare the public key derived from d with x. This occurs when an OKP private JWK supplies non-corresponding x and d components. As a result, identity derived from x can differ from operations performed with d. Consequently, if an integration also accepts private key parameters from a proof header without rejecting them, an attacker may use a stolen sender-constrained token without the legitimate private key. This issue is fixed in version 2.15.0.(CVE-2026-102275)

Summary

PyJWT 2.13.0 accepts compact JWS signature segments containing characters that are not in the Base64URL alphabet. Appending !!!! to a valid signature does not change the decoded signature bytes or authenticated claims, but it changes the serialized token and its SHA-256 hash. An application that indexes logout or revocation state by the raw token therefore rejects the logged-out token and accepts its no-key alternate serialization.

This report separates two issues: permissive compact-JWS decoding is the library behavior, while using raw serialized JWT text as a security identity is a dangerous application composition. A jti-indexed control blocks both representations.

Affected Version

Confirmed with PyJWT 2.13.0 on CPython 3.13. The mutation changes only the signature segment and requires no signing key.

End-to-End Reproduction

.venv-research/bin/python 06-practical-testing/revocation-bypass-lab.py

The loopback-only lab performs:

1. Issue a valid HS256 admin token.
2. Access /protected successfully.
3. Log out the canonical token and store SHA256(raw_token).
4. Confirm canonical replay returns HTTP 401.
5. Append !!!! to only the signature segment.
6. Confirm the mutated token has the same verified claims and signature bytes, a different raw hash, and receives HTTP 200.
7. Repeat with jti-indexed revocation and confirm both forms return HTTP 401.

Observed statuses for raw-token revocation were 200 -> logout -> 401 for the canonical token and 200 for the alternate serialization. The jti control returned 401 for both replays after logout.

Security Boundaries and Severity

This is not signature forgery: the attacker starts with a valid token and cannot alter its claims. Impact requires a consumer to bind revocation, replay state, rate limits, or cache identity to the raw compact string. Under that composition, an authenticated user can bypass logout or token-specific revocation without the signing key. Medium is suggested for triage because the security impact is real but application-dependent.

Recommended Fix

• Reject signature segments containing characters outside [A-Za-z0-9_-].
• Reject padding and other non-canonical Base64URL encodings for compact JWS.
• Add regression tests proving malformed signature encodings fail before or during verification.
• Document that applications must use a semantic identifier such as jti, not the raw serialized token, for revocation and replay state.

Maintainer update — 2026-09-09

We reproduced the reported behavior on the verified master commit 8915570: appending !!!! to a valid compact-JWS signature segment is accepted, produces the same decoded signature bytes and claims, and changes the serialized token hash. Existing JWS verification controls pass. The behavior is present in the tested release range represented by tags 2.4.0, 2.8.0, 2.10.1, 2.12.1, and 2.13.0.

The security impact is conditional on an application using the raw serialized token as the identity for logout, revocation, replay, rate-limit, or cache state. Under that composition, an attacker who already holds a valid token can use an alternate serialization after the canonical string is revoked. This is not signature forgery or claim alteration; applications should use a semantic identifier such as jti for token identity.

The report is ready to be accepted as a draft for continued remediation. A narrow fix assessment recommends rejecting non-canonical Base64URL characters and padding in compact-JWS segments. No fix commit or release is claimed yet.

Maintainer update — 2026-09-09

The fix has been rebased onto the current master as e6f48401001609a8f99e71fcaf355fb895d508a8 and is ready to be pushed. Compact-JWS header, payload, and signature segments are now required to use the unpadded Base64URL alphabet and canonical re-encoding; a signature segment containing non-canonical characters such as !!!! is rejected…

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, PyJWT signature segment is affected because signature segment decoding accepts characters outside the canonical Base64URL representation. This occurs when non-Base64URL characters are appended to a valid compact JWS signature segment. As a result, base64url_decode produces the same signature bytes for different serialized segments. Consequently, raw-token revocation checks can fail to recognize an equivalent modified token. This issue is fixed in version 2.14.0.

TuxCare rebuilt pyjwt to address 6 CVEs. Fixed in 2.10.1.post5+tuxcare.

TuxCare rebuilt pyjwt to address 6 CVEs. Fixed in 2.8.0.post4+tuxcare.

TuxCare rebuilt pyjwt to address 7 CVEs. Fixed in 2.3.0.post4+tuxcare.

TuxCare rebuilt pyjwt to address 3 CVEs. Fixed in 1.7.1.post4+tuxcare.

These are all security issues fixed in the python313-PyJWT-2.15.1-1.1 package on the GA media of openSUSE Tumbleweed.

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102274: Malformed RSA JWK aborts parsing of an entire JWK Set (bsc#1283071).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).
• CVE-2026-103001: reused mutable options mapping can cause verification checks bypass on subsequent decode calls (bsc#1283829).

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102274: Malformed RSA JWK aborts parsing of an entire JWK Set (bsc#1283071).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).
• CVE-2026-103001: reused mutable options mapping can cause verification checks bypass on subsequent decode calls (bsc#1283829).

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102274: Malformed RSA JWK aborts parsing of an entire JWK Set (bsc#1283071).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102274: Malformed RSA JWK aborts parsing of an entire JWK Set (bsc#1283071).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).
• CVE-2026-103001: reused mutable options mapping can cause verification checks bypass on subsequent decode calls (bsc#1283829).

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102274: Malformed RSA JWK aborts parsing of an entire JWK Set (bsc#1283071).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).
• CVE-2026-103001: reused mutable options mapping can cause verification checks bypass on subsequent decode calls (bsc#1283829).

This update for python-PyJWT fixes the following issues:

• CVE-2026-101917: attacker traffic can amplify outbound requests to the configured JWKS endpoint (bsc#1283060).
• CVE-2026-101918: unauthenticated request can raise an exception that may produce an HTTP 500 response (bsc#1283061).
• CVE-2026-102267: forwarded credentials may be disclosed or verification keys may be substituted (bsc#1283064).
• CVE-2026-102268: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283065).
• CVE-2026-102269: raw-token revocation checks can fail to recognize an equivalent modified token (bsc#1283066).
• CVE-2026-102270: an attacker can cause intensive CPU consumption (bsc#1283067).
• CVE-2026-102271: an attacker who knows the public key can forge authenticated HMAC tokens (bsc#1283068).
• CVE-2026-102275: an attacker may use a stolen sender-constrained token without the legitimate private key (bsc#1283072).