CVE-2026-48526: PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed families are allowed

highCVSS 7.4CVE-2026-48526

CSIRTS triage

vendor: PyJWT product: PyJWT Authentication bypass

What: Public RSA keys can be accepted as HMAC secrets when algorithm families are mixed, allowing attackers to forge HS256 tokens.
Who is affected: Applications using PyJWT with algorithm family validation disabled or when public keys are exposed.
Urgency: High urgency; authentication bypass enables token forgery and is actively exploitable.
Action: Update PyJWT to a patched version that enforces strict algorithm family validation.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.4
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-48526

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-485260.40% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 33% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-48526	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

medium[UPDATE] [medium] Red Hat Ansible Automation Platform: Multiple vulnerabilitiescert-bund

Recent advisories for PyJWT

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2025-45768: pyjwt v2.10.1 was discovered to contain weak encryption. NOTE: this is disputed by the Supplie…msrc · 2026-08-06
mediumCVE-2026-48525: PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=f…msrc · 2026-08-06