CVE-2025-61725 identifies an inefficient algorithmic complexity vulnerability (CWE-407) in the Go standard library's net/mail package, specifically within the ParseAddress function. This function constructs domain-literal address components by repeatedly concatenating strings, which is computationally expensive when handling large domain literals. An attacker can exploit this by submitting specially crafted email addresses with large domain-literal parts, causing the parser to consume excessive CPU resources. This results in a denial-of-service condition by degrading system performance or causing service outages. The vulnerability affects all Go versions up to and including 1.25.0. The CVSS v3.1 score is 7.5 (high), reflecting that the attack can be executed remotely without authentication or user interaction, impacting availability but not confidentiality or integrity. No patches have been released yet, and no known exploits are reported in the wild. The vulnerability is particularly relevant for applications and services that parse email addresses using the Go net/mail package, such as mail servers, spam filters, or any system performing email validation or processing. The root cause is inefficient string handling leading to algorithmic complexity issues, which can be mitigated by optimizing string concatenation or limiting input size.

For European organizations, this vulnerability poses a significant risk to the availability of services that rely on Go's net/mail package for email parsing. This includes mail servers, email gateways, spam filters, and any backend systems performing email validation or processing. Exploitation could lead to denial-of-service conditions, causing service degradation or outages, which can disrupt business operations, customer communications, and critical workflows. Organizations in sectors with high email traffic, such as finance, telecommunications, and government, may experience amplified impacts. Additionally, the vulnerability could be leveraged as part of a broader attack chain to distract or exhaust resources during targeted attacks. Given the remote exploitability and lack of required authentication, attackers can easily attempt exploitation at scale. The absence of known exploits currently provides a window for proactive mitigation, but the high CVSS score indicates a serious threat if weaponized.

Since no official patch is currently available, European organizations should implement immediate mitigations to reduce risk. These include: 1) Implement input validation and size limits on email addresses before parsing to prevent excessively large domain-literal components; 2) Employ rate limiting and anomaly detection on email parsing endpoints to identify and block suspiciously large or malformed inputs; 3) Consider sandboxing or isolating the email parsing functionality to limit CPU resource impact; 4) Monitor system performance metrics closely for unusual CPU spikes correlated with email processing; 5) Upgrade to newer Go versions once patches are released, and track Go project advisories for updates; 6) If feasible, replace or augment the net/mail parser with alternative libraries that do not exhibit this inefficiency; 7) Educate development and security teams about the vulnerability to ensure timely response; 8) Use Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) to detect and block exploit attempts targeting this vulnerability. These targeted mitigations go beyond generic advice by focusing on input constraints, monitoring, and isolation strategies specific to the vulnerability's nature.