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CVE-2026-33544

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances

7.7 HighFix available

Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
Low
User interaction
Required

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
None

Exploit likelihood

0.35%Up 0.3 points since Apr 3, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.7

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances

Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.

Record
CVE-2026-33544
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Weakness
CWE-362
Updated
2026-11-02
EUVDEUVD-2026-18254 7.7

Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.

Record
EUVD-2026-18254
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-9q5m-jfc4-wc92 7.7

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances

Summary

All three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity.

Details

The OAuthBrokerService.GetService() returns a single shared instance per provider for every request. The OAuth flow stores intermediate state as struct fields on this singleton:

Token storage — generic_oauth_service.go line 96:

generic.token = token  // Shared mutable field on singleton

Verifier storage — generic_oauth_service.go line 81:

generic.verifier = verifier  // Shared mutable field on singleton

In the callback handler oauth_controller.go lines 136–143, the code calls:

err = service.VerifyCode(code)                       // line 136 — stores token on singleton
// ... race window ...
user, err := controller.broker.GetUser(req.Provider)  // line 143 — reads token from singleton

Between these two calls, a concurrent request's VerifyCode() can overwrite the token field, causing GetUser() → Userinfo() to fetch the wrong user's identity claims.

The same pattern exists in all three implementations:

PoC

Race scenario (two concurrent OAuth callbacks):

  1. User A and User B both click "Login with GitHub" on the same tinyauth instance
  2. Both are redirected to GitHub, authorize, and GitHub redirects both back with authorization codes
  3. Both callbacks arrive at tinyauth nearly simultaneously:
Timeline:
  t0: Request A → service.VerifyCode(codeA) → singleton.token = tokenA
  t1: Request B → service.VerifyCode(codeB) → singleton.token = tokenB  (overwrites tokenA)
  t2: Request A → broker.GetUser("github")  → Userinfo() reads singleton.token = tokenB
  t3: Request A receives User B's identity (email, name, groups)

User A now has a tinyauth session with User B's email, gaining access to all resources User B is authorized for via tinyauth's ACL.

PKCE verifier DoS variant: Even with PKCE, concurrent oauthURLHandler calls overwrite the verifier field, causing VerifyCode() to send the wrong verifier to the OAuth provider, which rejects the exchange.

Static verification: Run Go's race detector on a test that calls VerifyCode and Userinfo concurrently on the same service instance — the -race flag will flag data races on the token and verifier fields.

Go race detector confirmation: Running a concurrent test with go test -race on the singleton service detects 4 data races on the token and verifier fields. Without the race detector, measured token overwrite rate is 99.9% (9,985/10,000 iterations).

Test environment: tinyauth v5.0.4, commit 592b7ded, Go race detector + source code analysis

Impact

An attacker who…

Record
GHSA-9q5m-jfc4-wc92
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Weakness
CWE-362
Updated
2026-11-02
NVD 7.7

Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.

Record
CVE-2026-33544
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Weakness
CWE-362
Updated
2026-11-02
OSV 7.7

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances

Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.

Record
CVE-2026-33544
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Weakness
CWE-362
Updated
2026-11-02
OSVGHSA-9q5m-jfc4-wc92 7.7

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances

Summary

All three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity.

Details

The OAuthBrokerService.GetService() returns a single shared instance per provider for every request. The OAuth flow stores intermediate state as struct fields on this singleton:

Token storage — generic_oauth_service.go line 96:

generic.token = token  // Shared mutable field on singleton

Verifier storage — generic_oauth_service.go line 81:

generic.verifier = verifier  // Shared mutable field on singleton

In the callback handler oauth_controller.go lines 136–143, the code calls:

err = service.VerifyCode(code)                       // line 136 — stores token on singleton
// ... race window ...
user, err := controller.broker.GetUser(req.Provider)  // line 143 — reads token from singleton

Between these two calls, a concurrent request's VerifyCode() can overwrite the token field, causing GetUser() → Userinfo() to fetch the wrong user's identity claims.

The same pattern exists in all three implementations:

PoC

Race scenario (two concurrent OAuth callbacks):

  1. User A and User B both click "Login with GitHub" on the same tinyauth instance
  2. Both are redirected to GitHub, authorize, and GitHub redirects both back with authorization codes
  3. Both callbacks arrive at tinyauth nearly simultaneously:
Timeline:
  t0: Request A → service.VerifyCode(codeA) → singleton.token = tokenA
  t1: Request B → service.VerifyCode(codeB) → singleton.token = tokenB  (overwrites tokenA)
  t2: Request A → broker.GetUser("github")  → Userinfo() reads singleton.token = tokenB
  t3: Request A receives User B's identity (email, name, groups)

User A now has a tinyauth session with User B's email, gaining access to all resources User B is authorized for via tinyauth's ACL.

PKCE verifier DoS variant: Even with PKCE, concurrent oauthURLHandler calls overwrite the verifier field, causing VerifyCode() to send the wrong verifier to the OAuth provider, which rejects the exchange.

Static verification: Run Go's race detector on a test that calls VerifyCode and Userinfo concurrently on the same service instance — the -race flag will flag data races on the token and verifier fields.

Go race detector confirmation: Running a concurrent test with go test -race on the singleton service detects 4 data races on the token and verifier fields. Without the race detector, measured token overwrite rate is 99.9% (9,985/10,000 iterations).

Test environment: tinyauth v5.0.4, commit 592b7ded, Go race detector + source code analysis

Impact

An attacker who…

Record
GHSA-9q5m-jfc4-wc92
CVSS 3.1
7.7 HighCVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N
Weakness
CWE-362
Updated
2026-11-02
OSVGO-2026-5296 No score

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances in github.com/steveiliop56/tinyauth

Tinyauth has OAuth account confusion via shared mutable state on singleton service instances in github.com/steveiliop56/tinyauth

Record
GO-2026-5296
Updated
2026-11-02
OSVopenSUSE-SU-2026:21483-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

  • GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
  • GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
  • GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
  • GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
  • GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
  • GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
  • GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
  • GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
  • GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
  • GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
  • GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
  • GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
  • GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
  • GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
  • GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
  • GO-2026-5933 GHSA-3g4q-2f67-2gvh
  • GO-2026-5934 GHSA-59qp-cfj3-rp64
  • GO-2026-5935 GHSA-7856-g3gv-9wq8
  • GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
  • GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
  • GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
  • GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
  • GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
  • GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
  • GO-2026-5942 CVE-2026-46600
  • GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
  • GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
  • GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
  • GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
  • GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
  • GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
  • GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
  • GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
  • GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
  • GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
  • GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
  • GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
  • GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
  • GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
  • GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
  • GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
  • GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
  • GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
  • GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
  • GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
  • GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
  • GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
  • GO-2026-5969 GHSA-g936-7jqj-mwv8
  • GO-2026-5970 CVE-2026-56852
  • GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
  • GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
  • GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
  • GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
  • GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
  • GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
  • GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
  • GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
  • GO-2026-5981 GHSA-mqxv-9rm6-w8qc
  • GO-2026-5982 GHSA-pqg7-v6wh-3pfp
  • GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
  • GO-2026-5985 GHSA-7rx3-5wx3-5v76
  • GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
  • GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
  • GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
  • GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
  • GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
  • GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
  • GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
  • GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
  • GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
  • GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
  • GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
  • GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
  • GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
  • GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
  • GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
  • GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…
Record
openSUSE-SU-2026:21483-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
github.com/steveiliop56/tinyauth
Go
 before 1.0.1-0.20260401140714-fc1d4f2082a5
1.0.1-0.20260401140714-fc1d4f2082a5
govulncheck-vulndb
openSUSE:Leap 16.0
From an advisory covering 1734 CVEs
 before 0.0.20260723T184607-160000.1.1
0.0.20260723T184607-160000.1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-33544 is a high vulnerability (CVSS 7.7) in Steveiliop56 Tinyauth, published April 1, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.35%, the 28th percentile. Fixed in github.com/steveiliop56/tinyauth 1.0.1-0.20260401140714-fc1d4f2082a5.

References

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