CVE-2026-46727: Ruby-lang Ruby Use-After-Free Vulnerability

CVE-2026-46727 Overview

CVE-2026-46727 is a race condition vulnerability in Ruby that leads to a use-after-free in the pthread-based getaddrinfo timeout handler. The flaw resides in rb_getaddrinfo within ext/socket/raddrinfo.c and affects Ruby 4 versions before 4.0.5. A remote attacker who can delay Domain Name System (DNS) responses near a user-specified timeout can crash any Ruby process that calls Addrinfo.getaddrinfo(..., timeout:) or Socket.tcp(..., resolv_timeout:). Memory-corruption-based exploitation is theoretically possible. The attack can be delivered through a crafted authoritative DNS server or a malicious recursive resolver positioned in the resolution path.

Critical Impact

Remote attackers controlling DNS response timing can crash Ruby processes and potentially achieve memory corruption against any application using timeout-enabled name resolution.

Affected Products

• Ruby-lang Ruby 4.0.0 through 4.0.4
• Applications calling Addrinfo.getaddrinfo with the timeout: parameter
• Applications calling Socket.tcp with the resolv_timeout: parameter

Discovery Timeline

• 2026-05-20 - Ruby project publishes advisory for CVE-2026-46727
• 2026-05-22 - CVE-2026-46727 published to NVD
• 2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-46727

Vulnerability Analysis

The vulnerability is a Time-of-Check Time-of-Use (TOCTOU) class race condition [CWE-362] in Ruby's socket extension. When a caller invokes name resolution with a timeout, Ruby spawns a pthread to perform getaddrinfo and arms a timer to abort the operation if the network response is slow. If the DNS response arrives at nearly the same instant the timeout fires, the timeout handler and the resolver thread both attempt to manage the same addrinfo allocation. The resolver thread frees memory the timeout path still references, producing a use-after-free condition.

The impact ranges from immediate process crash through SIGSEGV to potential heap memory corruption. Long-running Ruby services such as web applications, background job workers, and network proxies that resolve attacker-influenced hostnames are exposed. High attack complexity reflects the precise timing required to win the race, but a network-positioned attacker can repeatedly probe until the race is won.

Root Cause

The root cause is missing synchronization between the pthread executing getaddrinfo and the timeout cancellation path in rb_getaddrinfo. Ownership of the result buffer is not transferred atomically when the timeout expires, allowing concurrent free and use of the same heap object.

Attack Vector

Exploitation requires the attacker to control or influence DNS responses for a hostname the Ruby application resolves. A crafted authoritative server, a compromised recursive resolver, or an on-path network attacker can deliberately delay responses to land within the timeout window. No authentication or user interaction is required. See the Ruby Security Advisory and HackerOne Report #3607434 for additional technical context.

Detection Methods for CVE-2026-46727

Indicators of Compromise

• Unexpected Ruby process crashes with SIGSEGV or SIGABRT correlated with outbound DNS activity
• Core dumps showing fault addresses inside libc allocator routines invoked from rb_getaddrinfo
• Repeated short-lived DNS queries to the same hostname followed by abnormal process termination
• Resolver responses arriving with latency clustered around the configured timeout: or resolv_timeout: value

Detection Strategies

• Audit Ruby codebases for calls to Addrinfo.getaddrinfo and Socket.tcp using the timeout: or resolv_timeout: keyword arguments
• Monitor process supervisors such as systemd, Kubernetes, and Passenger for elevated Ruby worker restart rates
• Capture and analyze DNS traffic for response latency that consistently approaches application-defined timeouts
• Correlate application stack traces from crash reporters with the ext/socket/raddrinfo.c call path

Monitoring Recommendations

• Forward Ruby application crash telemetry and core dump metadata to a centralized log platform for anomaly analysis
• Track DNS resolver response time distributions and alert on bimodal patterns indicative of timeout manipulation
• Enable address sanitizer or hardened allocator instrumentation in staging environments to surface use-after-free conditions during testing

How to Mitigate CVE-2026-46727

Immediate Actions Required

• Upgrade all Ruby 4.x installations to Ruby 4.0.5 or later as the definitive remediation
• Inventory dependencies and gems that pass timeout: or resolv_timeout: to socket APIs and prioritize their hosts for patching
• Restrict outbound DNS resolution to trusted resolvers to reduce attacker influence over response timing
• Restart long-running Ruby workers after patching to ensure no vulnerable interpreter remains resident in memory

Patch Information

The Ruby core team released Ruby 4.0.5 to address CVE-2026-46727. The fix corrects ownership and synchronization of the addrinfo allocation between the resolver pthread and the timeout handler in ext/socket/raddrinfo.c. Patch details and download links are available in the Ruby Security Advisory.

Workarounds

• Remove the timeout: and resolv_timeout: keyword arguments from Addrinfo.getaddrinfo and Socket.tcp calls until patching is complete
• Implement DNS resolution timeouts at the resolver or network layer rather than in Ruby code
• Route DNS through an internal caching resolver that enforces strict response time bounds and rejects abnormally delayed answers
• Run Ruby workloads behind process supervisors that automatically restart crashed workers to limit denial-of-service impact

# Verify the installed Ruby version is patched
ruby --version
# Expected: ruby 4.0.5 or later

# Upgrade via rbenv
rbenv install 4.0.5
rbenv global 4.0.5

# Upgrade via package manager (Debian/Ubuntu example)
sudo apt update && sudo apt install --only-upgrade ruby