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CVE-2026-61845 represents a critical high-severity vulnerability discovered in the Crass CSS parser for Ruby.
The flaw originates from how the library processes numerical values expressed in CSS scientific notation.
Specifically, when Crass encounters excessively large numeric exponents within untrusted CSS style strings,
it attempts to convert these values using unbounded exponentiation prior to any boundary clamping logic.
Because the parser fails to impose strict limits or validation checks on the exponent size during processing,
an attacker can supply a specially crafted CSS payload containing massive exponents.
During the conversion phase, the underlying parser routines allocate disproportionate amounts of CPU cycles
and memory resources to compute the resulting numerical representation before clamping it to Float::MAX.
This lack of control over recursion depth and intermediate data structures results in severe resource exhaustion.
When an application utilizes vulnerable versions of Crass to parse attacker-controlled CSS strings,
even a single tiny input payload can trigger excessive memory allocation and CPU locking.
Consequently, the host application or server process becomes unresponsive, leading to a denial of service (DoS).
The vulnerability impacts the core parsing mechanism, making any web application accepting raw CSS input vulnerable.
Because parsing happens synchronously in many contexts, the thread or worker handling the request hangs indefinitely.
This can exhaust available system memory, cause Out-Of-Memory (OOM) crashes, or trigger cascading failures across services.
Mitigating this behavior requires limiting input size, validating numeric tokens, and upgrading the library.
Developers must understand that CSS parsers handling untrusted inputs are frequent targets for resource exhaustion.
Without proper bounds checking on numeric values and exponent magnitudes, parsers remain susceptible to abuse.
The discovery of this issue highlights the importance of robust input sanitization and defensive parsing techniques.
Updating to the secure release resolves the unbounded exponentiation flaw by implementing proper constraints.
Security teams should audit all dependencies utilizing Crass to ensure protection against this denial of service vector.
DailyCVE Form:
Platform: Crass Ruby gem
Version: Prior 1.0.7
Vulnerability : Denial of service
Severity: High severity
date: June 2026
Prediction: Already patched version
What Undercode Say:
Bash Commands and Codes
Check installed version of crass gem bundle exec gem list crass Update crass gem to version 1.0.7 or higher bundle update crass Run test suite to verify dependency integrity bundle exec rake test
Exploit: (Educational Purposes!)
Example of malicious CSS payload demonstrating unbounded exponentiation
require 'crass'
Malicious CSS string with an extremely large numeric exponent
malicious_css = 'body { width: 1e999999px; }'
Parsing this string forces disproportionate CPU and memory consumption
begin
Crass.parse(malicious_css)
rescue StandardError => e
puts "Parser failed or consumed excessive resources: {e.message}"
end
Protection: from this CVE
To protect applications against CVE-2026-61845, developers must immediately upgrade the `crass` gem to version 1.0.7 or later where bounds checks and clamping logic have been properly implemented. Additionally, applications should implement input length limits, timeouts on CSS parsing operations, and rate limiting on endpoints that process untrusted user-supplied style sheets.
Impact:
Successful exploitation of this vulnerability allows unauthenticated remote attackers to trigger severe denial of service (DoS) conditions against applications parsing user-controlled CSS strings. By submitting a minimal payload with unbounded exponents, an attacker can exhaust server CPU and memory resources, causing application crashes, thread starvation, and service unavailability without requiring privileged access.
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Sources:
Reported By: github.com
Extra Source Hub:
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