CVE-2026-729166.3MediumCWE-918

CVE-2026-72916: Mastodon: SSRF Protection Bypass via IPv4-compatible IPv6 Addresses

mastodon

Affected: mastodon · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

1.0%probability of exploitation in the next 30 days

62nd percentile

050100

Higher than 62% of scored CVEs

6.3MediumCVSS 4.0

LowMediumHighCrit.

DescriptionCVE.org

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

mastodon · mastodon< 4.4.21; >= 4.5.0-beta.1, < 4.5.14; >= 4.6.0-beta.1, < 4.6.4

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Server-Side Request Forgery
Vendor: mastodon
Published: August 2026
Band: Unlikely (under 1%), August 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-72916 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.