CVE-2026-27820
It was discovered that the Net::IMAP client in Ruby did not properly sanitize Symbol arguments passed to IMAP commands. A remote attacker controlling a malicious IMAP server, or able to influence command arguments, could use this to inject arbitrary IMAP commands via CRLF sequences. (CVE-2026-42258) It was discovered that the Zlib::GzipReader in Ruby did not correctly ensure sufficient buffer capacity in the zstream_buffer_ungets function. An attacker could use this to craft a gzip stream that, when processed, could cause a buffer overflow, resulting in memory corruption and possibly arbitrary code execution. (CVE-2026-27820)
CSIRTS triage
- What
- Vulnerabilities in Ruby could allow remote code execution and memory corruption.
- Who is affected
- Users of Ruby applications that utilize the affected components.
- Urgency
- Remediation is urgent due to the potential for severe impacts from exploitation.
- Action
- Users should update Ruby to the latest version.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.56% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 43% of all EPSS-scored CVEs.
Advisory coverage (2)
- medium[UPDATE] [medium] Ruby: Vulnerability allows Denial of Servicecert-bund · 2026-07-17
- unknownUSN-8556-1: Ruby vulnerabilitiesubuntu · 2026-07-16
External references
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[](https://www.csirts.com/cve/CVE-2026-27820)