CVE-2026-108555 in PairDrop
Summary
by MITRE • 10/10/2026
PairDrop through 1.11.2 contains an IP spoofing vulnerability in Peer._setIP that allows remote attackers to join other networks' discovery rooms by supplying a forged cf-connecting-ip header. Attackers who know a victim's public IP can appear as a local device on self-hosted instances not behind Cloudflare to send or receive files.
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Analysis
by VulDB Data Team • 10/10/2026
The vulnerability identified in PairDrop versions through 1.11.2 represents a critical failure in network identity verification, specifically within the Peer._setIP function. This flaw stems from an improper validation of incoming HTTP headers that are intended to convey client IP addresses when the application is deployed behind reverse proxies or content delivery networks like Cloudflare. By exploiting this trust relationship without adequate sanitization, remote attackers can inject a forged cf-connecting-ip header into their requests. The server blindly accepts this value as the true source address of the connection, leading to an IP spoofing condition where the attacker's actual network location is masked by a fabricated one. This mechanism bypasses standard access controls that rely on client IP addresses for authentication or authorization decisions within the application logic.
The operational impact of this vulnerability allows malicious actors to manipulate the discovery and pairing mechanisms inherent to PairDrop, which relies heavily on local network proximity for secure file transfers. In environments where instances are self-hosted and not protected by Cloudflare, an attacker who has knowledge of a victim's public IP address can spoof that specific IP during their connection attempt. Consequently, the application perceives the attacker as being physically present in the same local area network as the victim. This false perception enables the attacker to join discovery rooms intended for legitimate local users, thereby gaining unauthorized access to initiate file transfers or receive sensitive data from unsuspecting victims who believe they are interacting with a trusted peer on their own network segment.
From a classification perspective, this issue aligns closely with CWE-287, which describes Improper Authentication, as the system fails to correctly verify the identity of the client based on its IP address. Furthermore, it relates to CWE-346 regarding Origin Untrustworthiness, since the application trusts an external header without sufficient validation against known proxy configurations or internal network ranges. In terms of adversary tactics, this exploitation technique mirrors aspects of ATT&CK T1098, specifically SSH Host Impersonation or similar identity spoofing techniques used to gain unauthorized access by masquerading as a trusted entity within the infrastructure. The ability to appear as a local device fundamentally undermines the security model that assumes physical proximity equates to trustworthiness in peer-to-peer file sharing applications.
Mitigation strategies must focus on strict validation of source IP addresses and proper configuration of reverse proxy settings. Administrators should ensure that their web servers or load balancers are configured to only accept trusted headers from known, authorized upstream proxies rather than allowing any client to supply them directly. Implementing allowlists for internal network ranges can also help restrict which IPs are considered valid for local discovery features. Additionally, upgrading to a patched version of PairDrop is essential if available, as developers typically address such header injection flaws by implementing rigorous checks that verify the cf-connecting-ip against actual connection metadata or disabling reliance on this header entirely when not behind a verified proxy chain. Regular security audits and penetration testing should be conducted to identify similar trust boundary violations in other components of the application stack.