Cyber Resilience

CVE-2026-27962

Authlib ≤ 1.6.9

Public PoC
Published
16 March 2026
Modified
12 August 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS Score 0.0055 43th percentile
Risk Priority 67 floored blend · peak EPSS

Summary

CVE-2026-27962 is a critical-severity Improper Verification of Cryptographic Signature (CWE-347) vulnerability in Authlib Authlib. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Supply Chain Compromise (T1195); ranked at the 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SC-13 (Cryptographic Protection) and SI-7 (Software, Firmware, and Information Integrity) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-27962 is a JWK Header Injection vulnerability in the JWS implementation of Authlib, a Python library used to build OAuth and OpenID Connect servers. The flaw affects versions prior to 1.6.9. It occurs when the key=None parameter is passed to any JWS deserialization function, causing the library to extract and use a cryptographic key embedded in the attacker-controlled JWT jwk header field, enabling forged tokens to pass signature verification.

An unauthenticated attacker can exploit this vulnerability over the network with low complexity and no privileges required. By signing a JWT token with their own private key and embedding the matching public key in the jwk header, the attacker can produce arbitrary tokens that the server accepts as cryptographically valid. This bypasses authentication and authorization entirely, leading to high impacts on confidentiality and integrity, as reflected in the CVSS v3.1 score of 9.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N). The issue is classified under CWE-347.

The vulnerability has been patched in Authlib version 1.6.9. Security advisories recommend updating to this version or later to mitigate the issue. Relevant resources include the GitHub security advisory at https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5, release notes at https://github.com/authlib/authlib/releases/tag/v1.6.9, and the fixing commit at https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681.

OWASP Top 10 for Web (2025)

A04:2025 Cryptographic Failures

EU & UK References

Vulnerability Data

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…

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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.

CWE(s)
CWE-347

Related Threats

MITRE ATT&CK Enterprise Techniques

T1195 Supply Chain Compromise Initial Access
Adversaries may manipulate products or product delivery mechanisms prior to receipt by a final consumer for the purpose of data or system compromise.
attack.mitre.org →
T1195.002 Compromise Software Supply Chain Initial Access
Adversaries may manipulate application software prior to receipt by a final consumer for the purpose of data or system compromise.
attack.mitre.org →
T1542 Pre-OS Boot Stealth
Adversaries may abuse Pre-OS Boot mechanisms as a way to establish persistence on a system.
attack.mitre.org →
T1553 Subvert Trust Controls Defense Impairment
Adversaries may undermine security controls that will either warn users of untrusted activity or prevent execution of untrusted programs.
attack.mitre.org →
T1553.002 Code Signing Defense Impairment
Adversaries may create, acquire, or steal code signing materials to sign their malware or tools.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-28802Same product: Authlib Authlib
CVE-2024-37568Same product: Authlib Authlib
CVE-2026-28498Same product: Authlib Authlib
CVE-2025-59420Same product: Authlib Authlib
CVE-2025-68158Same product: Authlib Authlib
CVE-2025-61920Same product: Authlib Authlib
CVE-2026-28490Same product: Authlib Authlib
CVE-2026-41479Same product: Authlib Authlib
CVE-2026-41425Same product: Authlib Authlib
CVE-2025-62706Same product: Authlib Authlib

Affected Assets

authlib
authlib
≤ 1.6.9

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 14 hardening rules · 5 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

SC-13 Cryptographic Protection good match

Requiring cryptographic protection mechanisms forces correct signature verification to be implemented for data protection.

SI-7 Software, Firmware, and Information Integrity good match

Mandating integrity verification tools directly requires proper cryptographic signature checking to detect unauthorized changes.

SC-23 Session Authenticity partial match

Protecting session authenticity requires correct verification of cryptographic signatures or equivalent mechanisms.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.DS-01 mostly match
prevents

Digital signatures are explicitly cited to protect integrity of data-at-rest, so proper verification directly mitigates the weakness.

PR.DS-02 mostly match
prevents

Digital signatures are explicitly cited to protect integrity of data-in-transit, so proper verification directly mitigates the weakness.

ID.RA-09 partial match
prevents

Requires assessing authenticity and integrity of acquired assets, which commonly relies on signature verification but is limited to pre-acquisition.

PR.PS-06 partial match
prevents

Secure SDLC practices include code signing and signature verification requirements, addressing the weakness during development.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.24 Use of cryptography partial match
prevents

Establishing approved cryptographic solutions and usage practices lowers the probability that signature-verification steps will be omitted or incorrectly implemented.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (2 rules)
  • V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. prevents CWE-347
  • V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-347
Oracle Linux 9 (2 rules)
  • V-271525 OL 9 must have GPG signature verification enabled for all software repositories. prevents CWE-347
  • V-271523 OL 9 must check the GPG signature of locally installed software packages before installation. prevents CWE-347
RHEL 7 (2 rules)
  • V-204447 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-347
  • V-204448 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-347
RHEL 8 (1 rule)
  • V-230264 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-347
RHEL 9 (1 rule)
  • V-257822 RHEL 9 must have GPG signature verification enabled for all software repositories. prevents CWE-347

References