Dozzle: SSRF guard bypass via IPv6 transition addresses (6to4/NAT64/Teredo) in webhook notification dispatcher

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Dozzle is a realtime log viewer for docker containers. From 10.5.2 until 10.6.15, the isBlockedIP SSRF guard in internal/notification/dispatcher/webhook.go, used by safeDialContext for webhook notification URLs, does not inspect IPv4 addresses embedded in 6to4, NAT64, Teredo, or IPv4-compatible IPv6 addresses, allowing an authenticated user to reach loopback or link-local targets that the guard intends to block. This issue is fixed in version 10.6.15.

Source published

11 Aug 2026 16:52:13 UTC

Source modified

11 Aug 2026 19:57:12 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 2.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Dozzle is a realtime log viewer for docker containers. From 10.5.2 until 10.6.15, the isBlockedIP SSRF guard in internal/notification/dispatcher/webhook.go, used by safeDialContext for webhook notification URLs, does not inspect IPv4 addresses embedded in 6to4, NAT64, Teredo, or IPv4-compatible IPv6 addresses, allowing an authenticated user to reach loopback or link-local targets that the guard intends to block. This issue is fixed in version 10.6.15.

Source published

11 Aug 2026 17:19:16 UTC

Source modified

24 Oct 2026 15:10:00 UTC

Observed here

25 Oct 2026 15:19:03 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 2.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

## Summary The `isBlockedIP` SSRF guard in Dozzle's webhook notification dispatcher blocks loopback, link-local, multicast, and unspecified addresses but does not recognize IPv6 transition mechanism addresses (RFC 3056 6to4, RFC 6052 NAT64, RFC 4380 Teredo) that embed arbitrary IPv4 addresses. An authenticated user can bypass the guard to reach loopback services, cloud metadata endpoints (169.254.169.254), and other blocked ranges via webhook notification URLs. ## Affected component / versions - Package: `github.com/amir20/dozzle` - Affected versions: all versions with SSRF guard (current HEAD [`b9df313`](https://github.com/amir20/dozzle/commit/b9df31356fc024e6768a1aac605844dc041d95ee)) - Vulnerable code: `internal/notification/dispatcher/webhook.go` ## Details ### Root cause (CWE-918) [`internal/notification/dispatcher/webhook.go:32-51`](https://github.com/amir20/dozzle/blob/b9df31356fc024e6768a1aac605844dc041d95ee/internal/notification/dispatcher/webhook.go#L32-L51): ```go func isBlockedIP(ip net.IP) bool { if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() || ip.IsMulticast() || ip.IsInterfaceLocalMulticast() || ip.IsUnspecified() { return true } if v4 := ip.To4(); v4 != nil && zeroNetV4.Contains(v4) { return true } if ip.Equal(net.IPv4bcast) { return true } return false } ``` The guard intentionally allows RFC 1918 private ranges for self-hosted webhook targets, but blocks loopback (127.0.0.0/8, ::1), link-local (169.254.0.0/16, fe80::/10), and other non-routable addresses. IPv6 transition mechanism addresses bypass all these checks: | Mechanism | Prefix | Embeds | `isBlockedIP` result | |-----------|--------|--------|---------------------| | 6to4 | `2002::/16` | any IPv4 in bits 16-47 | `false` | | NAT64 WKP | `64:ff9b::/96` | any IPv4 in bits 96-127 | `false` | | Teredo | `2001:0000::/32` | any IPv4 in bits 96-127 | `false` | ### Reachability / trust boundary The `safeDialContext` function (line 53) resolves hostnames and checks each IP against `isBlockedIP` before establishing a TCP connection. This is used as the `DialContext` for the webhook HTTP client (line 115). Webhook URLs are configured by authenticated Dozzle users through the notification settings UI. The guard exists to prevent authenticated users from using webhook delivery as a proxy to reach the host machine's loopback services or cloud metadata endpoint. ### Attack chain 1. Authenticated user creates a webhook notification with URL `http://[2002:7f00:0001::1]:8080/` (6to4 embedding 127.0.0.1) 2. When a notification triggers, Dozzle's webhook dispatcher calls `safeDialContext` 3. The IPv6 address `2002:7f00:0001::1` is checked against `isBlockedIP` -- all predicates return false 4. Connection proceeds to the 6to4 relay which routes to 127.0.0.1 5. The webhook POST reaches the host's loopback services ## Impact An authenticated user can bypass the SSRF guard to: - Reach cloud metadata service at 169.254.169.254 via `2002:a9fe:a9fe::1` (6to4) to steal instance credentials - Reach localhost services via `64:ff9b::7f00:1` (NAT64) or `2002:7f00:0001::1` (6to4) - The webhook response body is logged at debug level but not returned to the user, making this a semi-blind SSRF (status code is returned) Note: RFC 1918 private ranges are intentionally allowed by the guard. This bypass specifically targets the blocked ranges (loopback and link-local/metadata) that the guard explicitly intends to prevent. ## Proof of concept Bypass vectors: ``` # 6to4 embedding 127.0.0.1 (bypasses IsLoopback) http://[2002:7f00:0001::1]:8080/ # NAT64 embedding 169.254.169.254 (bypasses IsLinkLocalUnicast) http://[64:ff9b::a9fe:a9fe]/latest/meta-data/ # 6to4 embedding 169.254.169.254 (bypasses IsLinkLocalUnicast) http://[2002:a9fe:a9fe::1]/latest/meta-data/ # Teredo embedding 127.0.0.1 http://[2001:0000:dead:beef:0000:0000:7f00:0001]:8080/ ``` Verification that `isBlockedIP` returns false for all vectors: ```go package main import ( "fmt" "net" ) func isBlockedIP(ip net.IP) bool { return ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() || ip.IsMulticast() || ip.IsInterfaceLocalMulticast() || ip.IsUnspecified() } func main() { for _, v := range []string{ "2002:7f00:0001::1", // 6to4 -> 127.0.0.1 "64:ff9b::a9fe:a9fe", // NAT64 -> 169.254.169.254 "2002:a9fe:a9fe::1", // 6to4 -> 169.254.169.254 } { ip := net.ParseIP(v) fmt.Printf("%-35s blocked=%v\n", v, isBlockedIP(ip)) } } // Output: all false ``` ## Remediation Add IPv6 transition mechanism prefix checks to `isBlockedIP`: ```go func isBlockedIP(ip net.IP) bool { // ... existing checks ... // IPv6 transition mechanisms embedding arbitrary IPv4 if len(ip) == net.IPv6len { if ip[0] == 0x20 && ip[1] == 0x02 { return true } // 6to4 if ip[0] == 0x00 && ip[1] == 0x64 && ip[2] == 0xff && ip[3] == 0x9b { return true } // NAT64 if ip[0] == 0x20 && ip[1] == 0x01 && ip[2] == 0x00 && ip[3] == 0x00 { return true } // Teredo } return false } ``` ## Credit Reported by tonghuaroot ([email protected]).

Source published

8 Sep 2026 18:11:56 UTC

Source modified

10 Sep 2026 15:25:38 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · LOW

Dozzle: SSRF guard bypass via IPv6 transition addresses (6to4/NAT64/Teredo) in webhook notification dispatcher in github.com/amir20/dozzle

Source published

10 Sep 2026 14:48:42 UTC

Source modified

10 Sep 2026 15:15:15 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.