CVE-2026-47156: MantisBT: SOAP API Authentication Bypass with Privilege Escalation to Administrator

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 52: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 52% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes mantisbt/mantisbt (Composer (PHP)) <= 2.28.3, fixed in 2.28.4. Check your lockfile, including transitive dependencies.

What it is

MantisBT is an open source bug tracker. Versions 2.28.3 and earlier contain a critical authentication bypass in the SOAP API's mcichecklogin() function. Any user knowing any valid cookiestring can authenticate as any other user (knowing their username), including the administrator, without knowing the target's password. The vulnerability is exploitable with zero prior access on default MantisBT installations because self-registration is enabled by default ($gallowsignup = ON). A self-registered user can use their own cookiestring (readable from their browser's MANTISSTRINGCOOKIE cookie after login) to impersonate the administrator via the SOAP API. The REST API is NOT affected. The REST API's AuthMiddleware derives the username server-side from the API token or session cookie, so the username cannot be spoofed. The Web UI is NOT affected. The Web UI authenticates via PHP session cookies (PHPSESSID) and validates the MANTISSTRINGCOOKIE against the logged-in user through authiscookievalid(). The username is derived server-side from the cookie, not supplied by the client. Version 2.28.4 contains a patch. No known workarounds are available.

From the GitHub advisory

MantisBT 2.28.3 and earlier contains a critical authentication bypass in the SOAP API's mcichecklogin() function. Any user knowing any valid cookiestring can authenticate as any other user (knowing their username), including the administrator, without knowing the target's password.

The vulnerability is exploitable with zero prior access on default MantisBT installations because self-registration is enabled by default ($gallowsignup = ON). A self-registered user can use their own cookiestring (readable from their browser's MANTISSTRINGCOOKIE cookie after login) to impersonate the administrator via the SOAP API.

The REST API is NOT affected. The REST API's AuthMiddleware derives the username server-side from the API token or session cookie, so the username cannot be spoofed.

The Web UI is NOT affected. The Web UI authenticates via PHP session cookies (PHPSESSID) and validates the MANTISSTRINGCOOKIE against the logged-in user through authiscookievalid(). The username is derived server-side from the cookie, not supplied by the client.

Impact - Full administrator access to the SOAP API from zero prior access (with self-registration enabled, which is the default) - Read/write all issues including private issues and notes across all projects - Full data exfiltration of all bug reports, attachments, user accounts (id, name, email), and non-private configuration values via the 71 SOAP operations available - Destructive operations: delete projects, issues, attachments, tags, categories, and versions - Data manipulation: create/modify issues, impersonate reporters, manage project structure - Chains with other vulnerabilities: the SOAP admin access enables exploitation of SOAP vulnerabilities that require administrator privileges

Weakness type: CWE-287, CWE-639.

Product: mantisbt/mantisbt (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-09-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.69% probability of exploitation activity in the next 30 days; percentile 52.

Timeline

• 2026-07-15 — GitHub-reviewed advisory GHSA-c2xg-qjqw-2v98 published (critical)
• 2026-09-09 — CVE record published by GitHub_M
• 2026-09-10 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-c2xg-qjqw-2v98 github.com
2. CVE.org record CVE-2026-47156 cve.org
3. NVD entry CVE-2026-47156 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. mantisbt.org mantisbt.org

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