"Claude Code's network sandbox funnels all outbound traffic through a local allowlist proxy, silently blocking any connection to unapproved hosts. According to vulnerability researcher Aonan Guan, two Claude Code network sandbox bypasses were discovered recently. One of them, tracked as CVE-2025-66479 and discovered by a different researcher, was related to the sandbox interpreting a setting to block all outbound traffic as 'allow everything'. This issue was fixed with an update released on November 26, 2025."
"The second sandbox bypass vulnerability, discovered by Guan, has been described as a SOCKS5 hostname null-byte injection issue. "The userʼs policy says allow only *.google.com. The attacker sends a hostname like attacker-host.com\x00.google.com. The filter sees the trailing .google.com and approves; the OS truncates at the null byte and dials attacker-host.com," Guan explained."
"According to Guan, the vulnerability was present in the Claude Code network sandbox from October 20, 2025, when the sandbox became generally available, until the release of version 2.1.90 in April, around the time he reported it through Anthropic's bug bounty program on HackerOne. The AI giant marked the vulnerability report as a duplicate. The researcher is displeased that Anthropic has not assigned a CVE identifier to this vulnerability and has not mentioned the issue in its release notes."
"Moreover, Guan noted that CVE-2025-66479 was assigned to the 'sandbox-runtime' library rather than Claude Code itself, and there was no warning to Claude Code users. "A team running [the vulnerable configuration] in production from October 20 through November 26 had no way to know the sandbox was effectively off, and no notice afterwards that it ha""
Claude Code’s network sandbox routes outbound traffic through a local allowlist proxy that blocks connections to unapproved hosts. Two bypasses were identified that could defeat this control. One issue involved a setting intended to block all outbound traffic being interpreted as allowing everything, tracked as CVE-2025-66479 and fixed in an update released on November 26, 2025. A second issue involved SOCKS5 hostname null-byte injection, where a crafted hostname could pass an allowlist check but be truncated by the operating system at a null byte, causing a connection to an attacker-controlled host. The null-byte issue existed from October 20, 2025 until version 2.1.90 in April, and the report was marked as a duplicate without a CVE or release-notes mention.
#cybersecurity #sandbox-escape #vulnerability-disclosure #outbound-traffic-filtering #cve-and-patching
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