{ "document": { "category": "csaf_base", "csaf_version": "2.0", "distribution": { "tlp": { "label": "WHITE" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this portal to enhance access to its information and vulnerabilities. The use of this information is subject to the following terms and conditions:\n\nThe vulnerabilities disclosed in this portal are gathered by NCSC-NL from a variety of open sources, which the user can retrieve from other platforms. NCSC-NL makes every reasonable effort to ensure that the content of this portal is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or real-time keeping up-to-date. NCSC-NL does not control nor guarantee the accuracy, relevance, timeliness or completeness of information obtained from these external sources. The vulnerabilities disclosed in this portal are intended solely for the convenience of professional parties to take appropriate measures to manage the risks posed to the cybersecurity. No rights can be derived from the information provided therein.\n\nNCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of the vulnerabilities disclosed in this portal. This includes damage resulting from the inaccuracy of incompleteness of the information contained in it.\nThe information on this page is subject to Dutch law. All disputes related to or arising from the use of this portal regarding the disclosure of vulnerabilities will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings." } ], "publisher": { "category": "coordinator", "contact_details": "cert@ncsc.nl", "name": "National Cyber Security Centre", "namespace": "https://www.ncsc.nl/" }, "title": "CVE-2026-33693", "tracking": { "current_release_date": "2026-03-30T19:11:46.079068Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-33693", "initial_release_date": "2026-03-25T20:59:52.026586Z", "revision_history": [ { "date": "2026-03-25T20:59:52.026586Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (4).| CWES updated (1)." }, { "date": "2026-03-25T20:59:56.773210Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-03-27T00:38:40.605438Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products created (1).| References created (3).| CWES updated (1)." }, { "date": "2026-03-27T00:38:47.287717Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-03-27T01:24:44.057577Z", "number": "5", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)." }, { "date": "2026-03-27T01:24:54.073880Z", "number": "6", "summary": "NCSC Score updated." }, { "date": "2026-03-27T20:56:27.352094Z", "number": "7", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-03-28T07:57:29.091747Z", "number": "8", "summary": "References created (1)." }, { "date": "2026-03-30T12:41:46.890281Z", "number": "9", "summary": "Unknown change." } ], "status": "interim", "version": "9" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<0.7.0-beta.9", "product": { "name": "vers:unknown/<0.7.0-beta.9", "product_id": "CSAFPID-5920663" } } ], "category": "product_name", "name": "lemmy" } ], "category": "vendor", "name": "LemmyNet" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-33693", "cwe": { "id": "CWE-918", "name": "Server-Side Request Forgery (SSRF)" }, "notes": [ { "category": "description", "text": "### Summary\n\nThe `v4_is_invalid()` function in `activitypub-federation-rust` (`src/utils.rs`) does not check for `Ipv4Addr::UNSPECIFIED` (0.0.0.0). An unauthenticated attacker controlling a remote domain can point it to 0.0.0.0, bypass the SSRF protection introduced by the fix for CVE-2025-25194 (GHSA-7723-35v7-qcxw), and reach localhost services on the target server.\n\n### Details\n\n**File:** `src/utils.rs` in `activitypub-federation-rust`\n**Function:** `v4_is_invalid(v4: Ipv4Addr) -> bool`\n\nThe function checks `is_private()`, `is_loopback()`, `is_link_local()`, `is_multicast()`, and `is_documentation()` — but omits `is_unspecified()`. On Linux, macOS, and Windows, TCP connections to 0.0.0.0 are routed to localhost (127.0.0.1).\n\nAdditionally, `::ffff:0.0.0.0` (IPv4-mapped IPv6) also bypasses because `v6_is_invalid()` calls `to_ipv4_mapped().is_some_and(v4_is_invalid)`, inheriting the same gap. Notably, `v6_is_invalid()` already includes `is_unspecified()` for native IPv6, making this an asymmetric oversight.\n\n**Independent secondary finding — DNS Rebinding TOCTOU:**\n`is_invalid_ip()` resolves DNS via `lookup_host()` for validation, but `reqwest` resolves DNS again for the actual connection. With TTL=0 DNS responses, an attacker can return a legitimate IP for the first resolution (passes check) and 127.0.0.1 for the second (reqwest connects to localhost). CVSS for rebinding alone: 4.8 (AC:H).\n\n### PoC\n\n**1. Logic Proof (reproduced from source):**\n\n```rust\nfn v4_is_invalid(v4: Ipv4Addr) -> bool {\n v4.is_private()\n || v4.is_loopback()\n || v4.is_link_local()\n || v4.is_multicast()\n || v4.is_documentation()\n // BUG: Missing || v4.is_unspecified()\n}\n\nassert_eq!(v4_is_invalid(Ipv4Addr::UNSPECIFIED), false); // 0.0.0.0 PASSES validation\nassert_eq!(v4_is_invalid(Ipv4Addr::LOCALHOST), true); // 127.0.0.1 correctly blocked\n```\n\n**2. OS Routing Verification:**\n\n```\n$ connect(0.0.0.0:80) → ConnectionRefused\n```\n\nConnectionRefused proves the OS routed to localhost (port 80 not listening). Any service on 0.0.0.0:PORT is reachable.\n\n**3. Attack Chain:**\n\n1. Attacker configures DNS: `evil.com A → 0.0.0.0`\n2. 2. Attacker sends ActivityPub activity referencing `https://evil.com/actor`\n3. 3. Library calls `verify_url_valid()` → `is_invalid_ip()` → resolves to 0.0.0.0\n4. 4. `v4_is_invalid(0.0.0.0)` returns `false` (BYPASS)\n5. 5. `reqwest` connects to 0.0.0.0 → reaches localhost services\n### Impact\n\n- **Direct:** Bypasses the SSRF protection layer for all ActivityPub federation traffic\n- - **Downstream:** 6+ dependent projects affected including Lemmy (13.7k stars), hatsu, gill, ties, fediscus, fediverse-axum\n- - **Attacker can:** Access cloud instance metadata (169.254.169.254 via rebinding), reach internal services on localhost, port scan internal infrastructure\n### Suggested Fix\n\n```rust\nfn v4_is_invalid(v4: Ipv4Addr) -> bool {\n v4.is_private()\n || v4.is_loopback()\n || v4.is_link_local()\n || v4.is_multicast()\n || v4.is_documentation()\n || v4.is_unspecified() // ADD: blocks 0.0.0.0\n || v4.is_broadcast() // ADD: blocks 255.255.255.255\n}\n```\n\nFor DNS rebinding TOCTOU, pin the resolved IP:\n\n```rust\nlet resolved_ip = lookup_host((domain, 80)).await?;\n// validate resolved_ip...\nlet client = reqwest::Client::builder()\n .resolve(domain, resolved_ip) // pin resolution\n .build()?;\n```", "title": "github - https://api.github.com/advisories/GHSA-q537-8fr5-cw35" }, { "category": "description", "text": "Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.7.0-beta.9, the `v4_is_invalid()` function in `activitypub-federation-rust` (`src/utils.rs`) does not check for `Ipv4Addr::UNSPECIFIED` (0.0.0.0). An unauthenticated attacker controlling a remote domain can point it to 0.0.0.0, bypass the SSRF protection introduced by the fix for CVE-2025-25194 (GHSA-7723-35v7-qcxw), and reach localhost services on the target server. Version 0.7.0-beta.9 patches the issue.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33693.json" }, { "category": "description", "text": "Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.7.0-beta.9, the `v4_is_invalid()` function in `activitypub-federation-rust` (`src/utils.rs`) does not check for `Ipv4Addr::UNSPECIFIED` (0.0.0.0). An unauthenticated attacker controlling a remote domain can point it to 0.0.0.0, bypass the SSRF protection introduced by the fix for CVE-2025-25194 (GHSA-7723-35v7-qcxw), and reach localhost services on the target server. Version 0.7.0-beta.9 patches the issue.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33693" }, { "category": "other", "text": "0.00044", "title": "EPSS" }, { "category": "other", "text": "4.0", "title": "NCSC Score" }, { "category": "other", "text": "There is cwe data available from source Nvd, Is related to (a version of) an uncommon product", "title": "NCSC Score top decreasing factors" } ], "product_status": { "known_affected": [ "CSAFPID-5920663" ] }, "references": [ { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-q537-8fr5-cw35" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33693.json" }, { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33693" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-q537-8fr5-cw35" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/LemmyNet/activitypub-federation-rust/commit/4ae8532b17bc35755240b7f55d4a5b7665351599" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/advisories/GHSA-7723-35v7-qcxw" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-q537-8fr5-cw35" }, { "category": "external", "summary": "Reference - github", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33693" } ], "scores": [ { "cvss_v3": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM" }, "products": [ "CSAFPID-5920663" ] } ], "title": "CVE-2026-33693" } ] }