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CVE-2026-48523— PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

Quick assessment

Affected
jpadilla pyjwt
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

pyjwt是美国José Padilla个人开发者的一个 Python 库。允许对 JSON Web 令牌（JWT）进行编码和解码。 pyjwt 2.9.0版本至2.12.1版本存在安全漏洞，该漏洞源于当使用PyJWK密钥调用jwt.decode()或jwt.decode_complete()时，验证器端算法允许列表被绕过，令牌头算法与调用者提供的算法允许列表进行比对，但签名验证使用绑定到PyJWK对象的算法而非头算法，导致攻击者可以使用不允许的算法签名，在JWT头中声明允许的算法，仍被接受。

CVSS 5.4 · Medium EPSS 0.17% · P6

Possible ATT&CK Techniques 1 AI

T1556 · Modify Authentication Process

Affected Version Matrix 1

VendorProduct Version RangeStatus
jpadilla pyjwt >= 2.9.0, < 2.13.0 affected
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I. Basic Information for CVE-2026-48523

Vulnerability Information
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Vulnerability Title
PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
pyjwt 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
pyjwt是美国José Padilla个人开发者的一个 Python 库。允许对 JSON Web 令牌（JWT）进行编码和解码。 pyjwt 2.9.0版本至2.12.1版本存在安全漏洞，该漏洞源于当使用PyJWK密钥调用jwt.decode()或jwt.decode_complete()时，验证器端算法允许列表被绕过，令牌头算法与调用者提供的算法允许列表进行比对，但签名验证使用绑定到PyJWK对象的算法而非头算法，导致攻击者可以使用不允许的算法签名，在JWT头中声明允许的算法，仍被接受。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
jpadilla pyjwt >= 2.9.0, < 2.13.0 -

II. Public POCs for CVE-2026-48523

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III. Intelligence Information for CVE-2026-48523

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Vendor Advisories for CVE-2026-48523 (1)

Same Patch Batch · jpadilla · 2026-05-28 · 5 CVEs total

CVE-2026-48526 7.4 HIGH PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed famil
CVE-2026-48525 5.3 MEDIUM PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b
CVE-2026-48522 4.2 MEDIUM PyJWKClient: missing scheme allowlist enables SSRF + token forgery via file://, ftp://, da
CVE-2026-48524 3.7 LOW PyJWT: PyJWKClient unbounded JWKS endpoint requests via attacker-controlled kid values (Do

IV. Related Vulnerabilities

Same product: pyjwt
Same vendor: jpadilla
Same weakness: CWE-347

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