NVD / CVE Program· CNA GitHub_M

CVE-2026-27962: Authlib JWS JWK Header Injection: Signature Verification Bypass

Noroxi assessment

Priority: Monitor (action score 36/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.55% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: authlib authlib 1.6.9.

Low priority for now. Upgrade to authlib authlib 1.6.9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attacker to forge arbitrary JWT tokens that pass signature verification. When key=None is passed to any JWS deserialization function, the library extracts and uses the cryptographic key embedded in the attacker-controlled JWT jwk header field. An attacker can sign a token with their own private key, embed the matching public key in the header, and have the server accept the forged token as cryptographically valid — bypassing authentication and authorization entirely. This issue has been patched in version 1.6.9.

CriticalCVSS 9.1 · v3.1—No exploit Fix available

Published: Mar 16, 2026
Updated: Sep 10, 2026
EPSS: 0.5% · 46th percentile
CWE: CWE-347

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 36 / 40 · 9.1 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.5%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 9.1; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
authlib	authlib	cpe:2.3:a:authlib:authlib

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

authlib authlibbefore 1.6.9

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

authlib authlib
- < 1.6.9affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	python-authlib	before 1.2.0-1+deb12u2	1.2.0-1+deb12u2
Debian:13	python-authlib	from 0	—
Debian:14	python-authlib	before 1.6.9-1	1.6.9-1
openSUSE:Leap 15.6	python-Authlib	before 1.3.1-150600.3.17.1	1.3.1-150600.3.17.1
openSUSE:Leap 16.0	python-Authlib	before 1.5.2-bp160.3.1	1.5.2-bp160.3.1
PyPI	authlib	before 1.6.9	1.6.9
SUSE:Linux Enterprise Module for Python 3 15 SP7	python-Authlib	before 1.3.1-150600.3.17.1	1.3.1-150600.3.17.1

Same product

authlib: all records

Other highest-scoring records for the same primary product.

CVE-2026-104056Authlib version 1.7.2 and below contains a vulnerability where discovery JSON metadata is cached without validation or issuer-origin binding
39Monitor
CVE-2026-96760Authlib library contains a signature‑verification bypass vulnerability
39Monitor
CVE-2026-116672Authlib RFC 7592 examples omit registration-access-token client binding
35Monitor

Published before and after this one in the same product

← EarlierCVE-2025-68158Jan 8, 2026 · Authlib: 1-click Account Takeover
35Monitor
← EarlierCVE-2026-28802Mar 6, 2026 · Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
30Monitor
Later →CVE-2026-28490Mar 16, 2026 · Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle
33Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
authlib authlib	1.6.9 · description	Vendor (CNA)
debian:python-authlib	1.2.0-1+deb12u2 · Debian:12	Package registry (OSV)
opensuse:python-Authlib	1.3.1-150600.3.17.1 · openSUSE:Leap 15.6	Package registry (OSV)
PyPI:authlib	1.6.9	Package registry (OSV)
suse:python-Authlib	1.3.1-150600.3.17.1 · SUSE:Linux Enterprise Module for Python 3 15 SP7	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

authlib/authlibcommit a5d4b2d

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-2880210 days apartAuthlib: Setting `alg: none` and a blank signature appears to bypass signature verification
30Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: None

Weakness class (CWE)

CWE-347 · Improper Verification of Cryptographic Signature

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

nvd-secondary

Root cause

The verifier takes the algorithm to verify with from the token’s own header. Untrusted data ends up deciding its own verification rule.

The bug in code

The whole CWE-347 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const claims = jwt.verify(token, publicKey);

Fixed

1const claims = jwt.verify(token, publicKey, {
2  algorithms: ["RS256"],
3  issuer: "https://id.example.com",
4  audience: "portal",
5});

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681

Show all references (9 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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