Nextcloud Server: Persistent denial of service via federated share injection
Summary
Nextcloud Server versions 22.0.0 through 34.0.0 allow an unauthenticated remote attacker to write arbitrary rows into the oc_share_external database table through the federated share endpoint. These rows persist indefinitely because there is no automatic cleanup, and they trigger three denial-of-service conditions on a 24-hour cycle for as long as they remain. The vulnerability affects availability only; the affected instance must expose the federated share endpoint to the attacker.
Affected
- Nextcloud Server 22.0.0 through 34.0.0 (according to CNA data)
- Default configuration: unaffected (according to CNA data)
- Exact trigger conditions: Unknown.
Fixed in
Unknown. Check advisory GHSA-5572-968j-v7g5 for the first patched release in each supported branch.
Workaround
- No vendor-documented workaround was retrieved.
- Restrict access to the federated share endpoint, for example by limiting federation or using a reverse proxy with access controls. Effectiveness: Unknown.
- Manual cleanup of unexpected or old entries in oc_share_external is possible, but not a verified fix. Create a database backup first.
Exploitation
- Exploited in the wild: No evidence found.
- CISA KEV: Not listed.
- Public exploit: None found in research, not conclusive.
- EPSS: 0.32 % (percentile 25).
Our recommendation
- Check whether the instance is internet-facing and whether federated sharing is enabled.
- Review the advisory GHSA-5572-968j-v7g5 and update to the first fixed release as soon as it is available.
- Inspect oc_share_external for unexpected or old entries and remove them after a database backup, since the rows keep causing recurring outages.
- Restrict federation or the federated share endpoint until patched.
- Monitor for recurring service disruptions every 24 hours.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- HackerOne report 3679640 hackerone.com
- Nextcloud security advisories (GitHub) github.com
- Nextcloud help: remove federated cloud share folder help.nextcloud.com
- SecurityFocus CVE-2026-77167 www.securityfocus.com
- VulDB 427432 vuldb.com
- Strix CVE-2026-77167 www.strix.ai
- threatint CVE-2026-77167 cve.threatint.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 11:57.
Original description (NVD)
Abusing the federated share endpoint, an attacker can write arbitrary rows into the oc_share_external database table. These rows persist indefinitely — there is no automatic cleanup mechanism. Three distinct denial-of-service conditions follow from this write primitive, all triggered from the same unauthenticated source and all self-renewing on a 24-hour cycle for as long as the injected rows remain in the database.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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