View at Official ubuntu advisory, NVD, CVE.org · CVE detail
Freshness: upstream tracker timestamp is available; use API updated time as primary recency signal.
CVE-2011-4815 medium priority: Ubuntu including 3 source packages (ruby1.8, ruby1.9, ruby1.9.1), 18 status rows across 6 suites (hardy, lucid, maverick, natty, oneiric, upstream): not-affected 8, released 5, DNE 4, ignored 1.
Ruby (aka CRuby) before 1.8.7-p357 computes hash values without restricting the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via crafted input to an application that maintains a hash table.