Bug 2482743 (CVE-2026-48523)

Summary: CVE-2026-48523 python-pyjwt: PyJWT: Verifier-side algorithm bypass leads to unauthorized information access
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: alinfoot, anpicker, anthomas, aprice, bbrownin, bdettelb, cahl, cmyers, dfreiber, dnakabaa, doconnor, dranck, drow, dschmidt, dtrifiro, eborisov, ehelms, erezende, ggainey, hasun, ilpinto, jburrell, jfula, jkoehler, jlanda, jmitchel, jowilson, jpasqual, jsamir, juwatts, jwong, kaycoth, kshier, lball, lbrazdil, lcouzens, ljawale, lphiri, ltomasbo, luizcosta, mbarnett, mhayden, mhulan, mminar, msilmser, ngough, nmoumoul, nweather, nyancey, oezr, omaciel, ometelka, osousa, pcreech, ptisnovs, rbiba, rbobbitt, rbryant, rchan, rhel-process-autobot, rjohnson, sdoran, simaishi, smallamp, smcdonal, sskracic, stcannon, syedriko, teagle, tmalecek, tpfromme, ttakamiy, veshanka, vkumar, watson-tool-maintainers, weaton, xdharmai, yguenane, ykashtan
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in PyJWT, a Python library for handling JSON Web Tokens (JWT). An attacker with control over a registered JSON Web Key (JWK) private key can bypass security checks by signing a token with a forbidden algorithm while claiming to use an allowed one. This allows the attacker to have the token accepted, potentially leading to unauthorized access or manipulation of sensitive information.
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Description OSIDB Bzimport 2026-05-28 16:02:17 UTC 
PyJWT is a JSON Web Token implementation in Python. From 2.9.0 to 2.12.1, there is a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow. This vulnerability is fixed in 2.13.0.