CVE-2026-34828

A session management vulnerability allows previously issued authenticated sessions to remain valid after sensitive account security changes, specifically password reset and password change. As a result, an attacker who has already obtained a valid session cookie can retain access to the account even after the victim changes or resets their password.

This weakens account recovery and session security guarantees. I reproduced the issue on listmonk v6.0.0.

Details

The application updates account credentials successfully, but existing active sessions are not revoked afterward.

This behavior was confirmed in two flows:

1. Password reset flow

   • A user resets their password through the forgot/reset flow.
   • The old password becomes invalid.
   • The new password works.
   • However, a session cookie issued before the reset remains valid and continues to authenticate successfully.

2. Authenticated password change flow

   • The same user logs in from two separate sessions.
   • Using session A, the password is changed through the authenticated profile endpoint.
   • The old password becomes invalid.
   • The new password works.
   • However, session B, issued before the password change, remains valid and continues to authenticate successfully.

From the source review, the reset flow consumes the reset token, updates the password, and creates a fresh session, but there does not appear to be any revocation of older sessions. The same applies to the profile password change flow.

Relevant code areas observed during review:

• cmd/auth.go, forgot/reset flow
• cmd/users.go, authenticated profile update flow
• internal/core/users.go, password update path

Additionally:

• It was verified that reset links are single-use.
• It was verified that password reset on a TOTP-enabled account still enforces TOTP on fresh login.
• However, already-issued sessions still remain valid after reset.

PoC

Case 1: Password reset does not revoke existing session

1. Create or use a normal user account.
2. Log in as that user and save the authenticated session cookie.
3. Trigger forgot-password for the account.
4. Use the emailed reset link and set a new password.
5. Verify:
   • the old password no longer works
   • the new password works
6. Replay the old pre-reset session cookie against an authenticated endpoint such as /api/profile.

Example validation request:

GET /api/profile HTTP/1.1
Host: 127.0.0.1:9000
Cookie: session=<old_pre_reset_session>

Observed result:

Server returns HTTP/1.1 200 OK
Response contains the authenticated user profile

Case 2: Password change does not revoke other active sessions

1. Log in twice as the same user and save two authenticated session cookies:

   • session A
   • session B

2. Using session A, change the password through the authenticated profile update endpoint.

3. Verify:

   • the old password no longer works
   • the new password works

4. Replay session B against an authenticated endpoint such as /api/profile.

Example password change request:

PUT /api/profile HTTP/1.1
Host: 127.0.0.1:9000
Cookie: session=<session_A>
Content-Type: application/json

{
  "name":"victim1",
  "email":"[email protected]",
  "password":"VictimChanged123"
}

Then validate session B:

GET /api/profile HTTP/1.1
Host: 127.0.0.1:9000
Cookie: session=<session_B>

Observed result:

• Server returns HTTP/1.1 200 OK
• Response contains the authenticated user profile

Attachment

listmonk-session-report.zip

This issue allows persistence of unauthorized access after credential recovery actions.

If an attacker has already stolen a valid session cookie through any means (for example malware, browser compromise, XSS, shared machine access, proxy leakage, or other session theft), the victim cannot fully recover the account by changing or resetting the password alone. The attacker’s existing session remains valid.

This impacts account recovery expectations and session security for all authenticated users, including users with TOTP enabled.

CVE-2026-34828 has a CVSS score of 7.1 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.1.1-0.20260329113754-1b5e8d38c778); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-34828? CVE-2026-34828 is a high-severity security vulnerability in github.com/knadh/listmonk (go), affecting versions >= 1.1.1-0.20241028090858-319053dd7a90, < 1.1.1-0.20260329113754-1b5e8d38c778. It is fixed in 1.1.1-0.20260329113754-1b5e8d38c778.
2. How severe is CVE-2026-34828? CVE-2026-34828 has a CVSS score of 7.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/knadh/listmonk are affected by CVE-2026-34828? github.com/knadh/listmonk (go) versions >= 1.1.1-0.20241028090858-319053dd7a90, < 1.1.1-0.20260329113754-1b5e8d38c778 is affected.
4. Is there a fix for CVE-2026-34828? Yes. CVE-2026-34828 is fixed in 1.1.1-0.20260329113754-1b5e8d38c778. Upgrade to this version or later.
5. Is CVE-2026-34828 exploitable, and should I be worried? Whether CVE-2026-34828 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34828 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34828? Upgrade github.com/knadh/listmonk to 1.1.1-0.20260329113754-1b5e8d38c778 or later.