CVE-2026-103001: PyJWT.decode() reintroduces options-dict mutation, enabling silent claim-verification bypass on dict reuse

PyJWT.decode()/decode_complete() mutates a caller-supplied options dict in place whenever verify_signature is falsy, adding verify_exp/verify_nbf/verify_iat/verify_aud/verify_iss/verify_sub/verify_jti keys directly onto that object. If application code reuses the same options dict across calls (a config object, a module-level constant, a wrapper’s self.options), a later call that explicitly sets verify_signature=True for a full, normal verification silently inherits the leftover verify_exp=False etc. from an earlier verify_signature=False call on the same object – and accepts an expired, wrong-audience, wrong-issuer, or wrong-subject token as valid with no exception. Signature verification itself is unaffected; this is specifically a claims-check bypass.

This is a regression of an already-fixed, closed issue: originally reported in #679 (2021), fixed in #743 (2022, via a shallow copy of options), and silently reintroduced by #1045 (merged 2025-03-05, a typing/logic refactor that dropped the 2022 shallow-copy line). It has been present since #1045 merged, so it likely shipped in several releases already in the wild.