How severe is CVE-2026-28498?

No CVSS score has been assigned to CVE-2026-28498 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-28498?

CVE-2026-28498 affects the following packages: authlib (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-28498?

Update authlib to 1.6.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28498 is resolved across your whole dependency graph.

How do I detect CVE-2026-28498 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for authlib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-28498 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-28498?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-28498 can be triaged on real exposure rather than presence alone.

Is CVE-2026-28498 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-28498 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-28498?

CVE-2026-28498 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 14th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-28498?

CVE-2026-28498 is classified as CWE-354 (CWE-354), CWE-573 (CWE-573), CWE-325 (CWE-325). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-28498 published, and has it been updated?

CVE-2026-28498 was published on March 16, 2026 and was last updated on September 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2026-28498: authlib

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28498.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected

🐍authlib

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`authlib`	all versions	1.6.9`pip install --upgrade 'authlib==1.6.9'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for authlib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update authlib to 1.6.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28498 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-28498 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-28498. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This IMPORTANT vulnerability in Authlib allows attackers to bypass OIDC ID Token integrity verification. The at_hash and c_hash validation fails open for unknown algorithms, accepting forged tokens as valid. Exploitation requires no authentication or user interaction. Impact is high to confidentiality and integrity.…

Product	Fixed in	Advisory
Red Hat Ansible Automation Platform 2.6	`ansible-automation-platform-26/lightspeed-chatbot-rhel9:1774417022`	RHSA-2026:6309
Red Hat Ansible Automation Platform 2.6	`ansible-automation-platform-26/lightspeed-chatbot-rhel9:1774417022`	RHSA-2026:6404
Red Hat Quay 3.10	`quay/quay-rhel8:1775169155`	RHSA-2026:6912
Red Hat Quay 3.12	`quay/quay-rhel8:1775253092`	RHSA-2026:6720
Red Hat Quay 3.15	`quay/quay-rhel8:1775169219`	RHSA-2026:6568
Red Hat Quay 3.16	`quay/quay-rhel9:1775069491`	RHSA-2026:6497
Red Hat Quay 3.16	`quay/quay-rhel9:1775169226`	RHSA-2026:6567

UbuntuCRITICAL

USN-8557-1Ubuntu

Frequently Asked Questions

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID

O3 Security · Impact-Aware SCA

Is CVE-2026-28498 in your dependencies?

O3 Security finds CVE-2026-28498 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works

CVE-2026-28498 — authlib