joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. in versions 1.7.1 and prior, joserfc accepts JWTs with trailing padding (==) which are not conforming to the JOSE specifications. This leads to malleability of the JWTs when consumed by joserfc. Depending on this application this might or not be an issue. This could lead to bypass of token revocation or anti-replay protection when implemented as a deny list of tokens or a deny list of token hashes. Note that ECDSA JWS are always malleable because of the malleability of ECDSA signatures (first test case in the code bellow). This makes a scheme which assumes that JWTs are not malleable brittle. However for other signatures (or MAC) schemes it might make sense to assume non malleability of the token. This issue has been fixed in version 1.7.2.

A flaw was found in joserfc, a Python library for JSON Object Signing and Encryption (JOSE) standards. This vulnerability allows the library to accept JSON Web Tokens (JWTs) that include non-standard trailing padding. An attacker could exploit this to create malleable JWTs, potentially bypassing security mechanisms like token revocation or anti-replay protection. This could lead to unauthorized access or continued use of tokens that should be invalid.

Moderate: The joserfc Python library, utilized across various Red Hat products, is susceptible to JWT malleability due to its handling of non-standard trailing padding. This flaw could enable an attacker to bypass token revocation or anti-replay mechanisms in applications that depend on the integrity of JWTs processed by vulnerable versions of the library. Red Hat Hardened Images 2026-07-30T00:00:00Z RHSA-2026:48758 jaeger-main-2.20.0-0.8.hum1 Lightspeed Core Fix deferred lightspeed-core/lightspeed-stack-rhel9 Migration Toolkit for Applications 8 Fix deferred mta/mta-solution-server-rhel9 OpenShift Lightspeed Fix deferred openshift-lightspeed/lightspeed-agentic-sandbox-rhel9 Red Hat Ansible Automation Platform 2 Fix deferred ansible-automation-platform-26/lightspeed-chatbot-rhel9 Red Hat Ansible Automation Platform 2 Fix deferred ansible-automation-platform-27/lightspeed-chatbot-rhel9 Red Hat Enterprise Linux command line assistant Not affected rhel-cla/rhel-knowledge-bridge-rhel10 Red Hat OpenShift Virtualization 4 Fix deferred container-native-virtualization/ocp-virt-validation-checkup-rhel9 Red Hat Satellite 6 Fix deferred satellite/foreman-mcp-server-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-62995 https://nvd.nist.gov/vuln/detail/CVE-2026-62995 https://github.com/authlib/joserfc/security/advisories/GHSA-5jhw-7jv7-qcqq