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Google's MCP Toolbox was found vulnerable to a DNS rebinding attack tracked as CVE-2026-9739, affecting deployments that use Server-Sent Events (SSE) under specification v2024-11-05. The flaw stemmed from a hardcoded permissive CORS header, Access-Control-Allow-Origin: *, left in the SSE initialization handler even after allowed-origins and allowed-hosts controls were introduced during beta. The issue is classified as CWE-942 and was reported to Google through cve-coordination@google.com, with public disclosure tied to GitHub issue #3053.
Researchers said the weakness could let an attacker abuse a victim's browser to access internal MCP Toolbox services and connected enterprise databases, potentially exposing sensitive data and enabling unauthorized queries. Google addressed the issue in pull request #3054 by removing the wildcard origin behavior and enforcing stricter origin validation. Organizations using MCP Toolbox are being urged to upgrade to the patched release, limit allowed origins to trusted domains, disable unnecessary SSE endpoints, audit internet-exposed SSE services, and watch for unusual internal request patterns that could indicate exploitation.
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The issue was fixed in pull request #3054 by removing the hardcoded Access-Control-Allow-Origin wildcard and enforcing stricter origin validation. The fix addressed the retained permissive CORS behavior in the SSE initialization handler.
The vulnerability was publicly disclosed through GitHub issue #3053, describing a permissive CORS wildcard in the MCP Toolbox SSE handler that enabled DNS rebinding attacks. Reporting says the flaw particularly affected SSE deployments under specification v2024-11-05.
The CVE entry states that CVE-2026-9739 was received by cve-coordination@google.com on May 27, 2026. The vulnerability affects Google APIs MCP Toolbox and involves a DNS rebinding issue in the SSE handler.
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Microsoft has published a cluster of DNS-related security advisories covering **remote code execution, denial of service, cache poisoning, heap overflow, and access-control bypass** conditions across Windows DNS Server and third-party DNS components. The newly listed issues include `CVE-2026-33278` for possible arbitrary code execution during **DNSSEC** validation, `CVE-2026-42959` for crashes triggered by malicious DNSSEC content, `CVE-2026-42960` for possible cache poisoning through promiscuous authority-section records, and `CVE-2026-42944` for a heap overflow involving multiple `NSID`, `COOKIE`, and `PADDING` **EDNS** options. Additional advisories describe degradation-of-service conditions tied to long EDNS option lists (`CVE-2026-41292`), unbounded name compression (`CVE-2026-44390`), and a "packet of death" affecting **DNSCrypt** (`CVE-2026-32792`). The disclosures also reference flaws in widely used DNS software, including a **BIND 9** resolver unbounded resend loop (`CVE-2026-5950`), invalid handling of `CLASS != IN` (`CVE-2026-5946`), and a **CoreDNS** ACL bypass (`CVE-2026-26017`). Earlier Microsoft advisories for Windows DNS Server remote code execution, including `CVE-2021-33754` and `CVE-2021-33746`, show that DNS services remain a recurring high-impact target because they are network-exposed and central to enterprise operations. For defenders, the combined set of advisories highlights the need to prioritize patching DNS infrastructure, review exposure of DNSSEC, EDNS, and DNSCrypt features, and monitor for service instability or anomalous DNS responses that could indicate exploitation attempts.
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Jul 12, 2026
NLnet Labs has addressed multiple vulnerabilities in the **Unbound** DNS resolver, including **`CVE-2026-33278`**, a high-severity flaw in the DNSSEC validator that can cause denial of service and potentially **remote code execution**. The bug affects Unbound versions **`1.19.1` through `1.25.0`** and stems from a deep-copy error that overwrites a destination pointer, later triggering a dangling-pointer dereference. The issue is tracked under **`CWE-416`** and **`CWE-672`** and carries high potential impact to confidentiality, integrity, and availability. Exploitation requires an attacker to control a malicious signed DNS zone and induce a vulnerable Unbound instance to query it while a **DS sub-query** is suspended because of **NSEC3 computational budget exhaustion**. Belgium's Centre for Cybersecurity warned that the Unbound vulnerabilities could enable denial-of-service and urged organizations to patch immediately. The vendor has fixed the issue in **Unbound `1.25.1`**, making upgrade a priority for operators using affected resolver versions.
Jun 29, 2026