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CVE-2026-48525— PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS

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 2.8.0版本至2.12.1版本存在安全漏洞，该漏洞源于在验证使用未编码有效载荷选项的分离JWS令牌时，PyJWT在强制执行分离有效载荷规则之前对紧凑序列化有效载荷段进行Base64URL解码，导致远程客户端可以提供任意大的Base64URL有效载荷段，即使签名无效也会强制CPU工作和内存分配，造成未经验证的拒绝服务攻击。

CVSS 5.3 · Medium EPSS 0.41% · P34

Affected Version Matrix 1

VendorProduct Version RangeStatus
jpadilla pyjwt >= 2.8.0, < 2.13.0 affected
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I. Basic Information for CVE-2026-48525

Vulnerability Information
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Vulnerability Title
PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS
Source: CVE Program / CVE List V5
Vulnerability Description
PyJWT is a JSON Web Token implementation in Python. From 2.8.0 to 2.12.1, when verifying detached JWS tokens using the unencoded-payload option ("b64": false, RFC 7797), PyJWT performs Base64URL decoding of the compact-serialization payload segment before enforcing the detached-payload rules. For b64=false, PyJWT later discards that decoded payload and replaces it with the caller-provided detached_payload. In practice, this turns the middle segment into an attacker-controlled “work amplifier”: a remote client can supply an arbitrarily large Base64URL payload segment that forces CPU work + memory allocations even if the signature is invalid. This creates an unauthenticated DoS vector against any endpoint that verifies detached JWS using PyJWT. This vulnerability is fixed in 2.13.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
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 2.8.0版本至2.12.1版本存在安全漏洞，该漏洞源于在验证使用未编码有效载荷选项的分离JWS令牌时，PyJWT在强制执行分离有效载荷规则之前对紧凑序列化有效载荷段进行Base64URL解码，导致远程客户端可以提供任意大的Base64URL有效载荷段，即使签名无效也会强制CPU工作和内存分配，造成未经验证的拒绝服务攻击。
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 >= 2.8.0, < 2.13.0 -

II. Public POCs for CVE-2026-48525

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III. Intelligence Information for CVE-2026-48525

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Vendor Advisories for CVE-2026-48525 (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-2026-48523 5.4 MEDIUM PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
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-400

V. Comments for CVE-2026-48525

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