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CVE Record

CVE-2026-28802: Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.

CriticalCVSS 9.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

Authlib versions 1.6.5 and 1.6.6 could accept a JWT claiming no signing algorithm with a blank signature, allowing signature verification bypass. Systems relying on Authlib for OAuth or OpenID Connect token validation may accept forged tokens. The issue is critical because network attackers need no privileges or user interaction. Fixed in 1.6.7.

Executive priority

Treat as urgent for internet-facing or SSO-integrated systems using affected Authlib versions. The business risk is unauthorized access or data exposure through token trust failure. Patch quickly, but scope work to confirmed Authlib 1.6.5 and 1.6.6 exposure.

Technical view

This is CWE-347 improper verification of cryptographic signature in Authlib >=1.6.5 and <1.6.7. The reported condition involved malicious JWTs using alg:none and an empty signature unexpectedly passing verification. CVSS 3.1 is 9.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Upstream identifies version 1.6.7 as patched.

Likely exposure

Exposure is limited to applications or packaged products using Authlib 1.6.5 or 1.6.6 for JWT, OAuth, or OpenID Connect token verification. Check direct Python dependencies, transitive dependencies, containers, and vendor packages. Authlib versions before 1.6.5 are not listed as affected in the provided sources.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. The vulnerability is remotely reachable when token verification is exposed through authentication flows. The high risk comes from possible trust bypass, not from evidence of in-the-wild exploitation in the provided sources.

Researcher notes

Do not assume all JWT libraries or all Authlib versions are affected. The evidence names Authlib 1.6.5 through before 1.6.7 and a specific alg:none plus blank-signature verification bypass. Public sources identify a patch, upstream commits, Red Hat tracking, and multiple Red Hat advisories.

Mitigation direction

  • Upgrade Authlib to version 1.6.7 or later.
  • Apply relevant vendor updates for packaged Authlib, including Red Hat advisories where applicable.
  • Review vendor guidance for any environment-specific mitigation or backport status.
  • Prioritize services that validate bearer tokens, ID tokens, or OAuth assertions.
  • Retest authentication and authorization flows after updating.

Validation and detection

  • Inventory deployed Authlib versions in applications, images, and packaged dependencies.
  • Confirm no runtime uses Authlib versions 1.6.5 or 1.6.6.
  • Check Red Hat advisory applicability for managed platform packages.
  • Review authentication logs for unusual token acceptance patterns if feasible.
  • Run regression tests covering rejected unsigned or invalidly signed JWTs.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-347: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-28802 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.1 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
13Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2redhat-SADP
7.7CVSS 4.0HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

7.7High
CVSS 4.0 vector shape for CVE-2026-28802Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPauthlib: Authlib: Signature verification bypass via malicious JWT allows unauthorized access
other:Red Hat severity ratingcvssV3_1
  • 2026-03-06T07:01:49.366Z: Reported to Red Hat.
  • 2026-03-06T06:44:26.402Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
authlibauthlib>= 1.6.5, < 1.6.7Listed
Weakness

CWE details

CWE-347

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-347 · source CWE mapping

Improper Verification of Cryptographic Signature

Improper Verification of Cryptographic Signature represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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