CVE-2026-55160 in Stringer
Summary
by MITRE • 09/28/2026
Stringer is a self-hosted, anti-social RSS reader. Prior to commit 75cb095, an unrestricted Server-Side Request Forgery (SSRF) vulnerability allows any authenticated user to force the Stringer server to send arbitrary HTTP/HTTPS requests to internal networks, localhost services, and cloud metadata endpoints (e.g. AWS IMDS 169.254.169.254). When self-service signup is enabled (Setting::UserSignup), even a low-privileged registered user can exploit this to scan internal services or steal cloud IAM credentials. This issue has been patched via commit 75cb095.
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Analysis
by VulDB Data Team • 09/28/2026
The vulnerability identified in the Stringer RSS reader represents a critical Server-Side Request Forgery (SSRF) flaw that compromises the integrity of self-hosted deployments, particularly those with internet-facing interfaces or internal network exposure. SSRF vulnerabilities occur when an application fetches a remote resource without validating the user-supplied URL, allowing attackers to induce the server to make HTTP requests to unexpected destinations. In this specific instance, prior to commit 75cb095, Stringer failed to properly restrict the destination addresses for outgoing requests initiated by authenticated users. This lack of input validation enabled any logged-in account to manipulate the application into contacting arbitrary internal services, localhost endpoints, or cloud provider metadata service interfaces such as AWS Instance Metadata Service (IMDS) at 169.254.169.254. The severity is significantly amplified when self-service signup is enabled via the Setting::UserSignup configuration, as it allows untrusted, low-privileged users to exploit this flaw without prior authentication barriers beyond basic account creation.
The operational impact of this vulnerability extends far beyond simple network reconnaissance. By forcing the server to interact with internal services, an attacker can map out the internal network topology and identify vulnerable applications running on localhost or within private subnets that are not directly exposed to the internet. More critically, access to cloud metadata endpoints allows for the exfiltration of sensitive infrastructure credentials. On platforms like AWS, Azure, or GCP, these endpoints provide temporary security credentials, IAM roles, and other configuration data necessary for instance operation. Compromise of this data can lead to full control over cloud resources, lateral movement within the network, and potential data breaches. This aligns with CWE-918, which classifies Server-Side Request Forgery as a weakness where web applications retrieve remote resources without validating user-supplied URL information, often leading to unauthorized access to internal systems or sensitive data exposure.
From an offensive security perspective, this vulnerability maps directly to the MITRE ATT&CK technique T1046, Network Service Discovery, and potentially T1528, Steal Application Access Token, depending on the cloud environment exploited. The ability to scan internal services facilitates reconnaissance, while access to metadata endpoints enables credential theft, which is a precursor to privilege escalation and persistent access within the compromised infrastructure. Even in environments where self-service signup is disabled, authenticated users with minimal privileges retain the capability to exploit this flaw, making it a significant risk for any deployment that does not strictly isolate internal services from web-facing applications or enforce rigorous network segmentation.
Mitigation strategies must focus on both immediate patching and long-term architectural hardening. The primary remediation involves applying commit 75cb095, which introduces proper validation mechanisms to restrict outgoing requests to allowed domains or IP ranges, effectively blocking access to internal networks and cloud metadata endpoints. Beyond the code fix, organizations should implement network-level controls such as firewall rules that prevent web servers from initiating connections to private IP address spaces (e.g., 10.x.x.x, 172.16.x.x-172.31.x.x, 192.168.x.x) and cloud metadata ranges unless explicitly required for legitimate functionality. Additionally, deploying a reverse proxy with strict egress filtering can provide an additional layer of defense by intercepting and validating outbound requests before they reach the application server. Regular security audits and penetration testing should be conducted to ensure that similar SSRF vectors are not present in other components of the RSS reader or associated infrastructure.