CVE-2026-58593

Description

NodeBB does not bind the claimed author of an inbound ActivityPub object to the authenticated remote actor. The inbound middleware verifies the HTTP-signature actor and checks the origin of object.id, but never validates that attributedTo corresponds to the sender. In the object mock, attributedTo is used directly as a uid, and actors.assert silently ignores numeric identifiers (filtering them out without re-deriving the uid), so a federated remote actor can set attributedTo to a bare numeric value such as 1 and have the resulting post or private message created with that local uid as author, including the administrator account. This lets a remote attacker forge posts and direct messages attributed to arbitrary local users. Requires the ActivityPub/federation feature to be enabled.

CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0019

Probability of exploitation

0.09%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-290 CWE-290

CWE-345 CWE-345

Affected Products

Vendor	Product	Versions
nodebb	nodebb	< 4.13.2

References

Exploits

https://github.com/NodeBB/NodeBB/blob/v4.13.2/src/activitypub/mocks.js https://github.com/bikini/exploitarium/tree/main/nodebb-activitypub-attributedto-local-uid-spoof-poc https://www.vulncheck.com/advisories/nodebb-activitypub-author-spoofing-via-unvalidated-attributedto-mapped-to-local-user

Frequently Asked Questions

What is CVE-2026-58593? +

NodeBB does not bind the claimed author of an inbound ActivityPub object to the authenticated remote actor. The inbound middleware verifies the HTTP-signature actor and checks the origin of object.id, but never validates that attributedTo corresponds to the sender. In the object mock, attributedTo is used directly as a uid, and actors.assert silently ignores numeric identifiers (filtering them out without re-deriving the uid), so a federated remote actor can set attributedTo to a bare numeric value such as 1 and have the resulting post or private message created with that local uid as author, including the administrator account. This lets a remote attacker forge posts and direct messages attributed to arbitrary local users. Requires the ActivityPub/federation feature to be enabled. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-58593? +

CVE-2026-58593 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0019, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-58593? +

CVE-2026-58593 affects products from nodebb, specifically: nodebb. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-58593? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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