{"data":{"id":"e4e75f53-a9f4-4246-9491-acab5ddc35ab","title":"From Training Exposure to Membership Evidence: A Controlled Study of OLMo 2","summary":"Researchers re-ran OLMo 2 1B's 50-billion-token mid-training stage, swapping in 7,814 matched document pairs with a coin flip deciding which copy was trained on. A single exposure raises a document's average likelihood but rarely identifies it: the reference-ratio attack reaches an AUC of 0.767 yet catches only 3.8% of members at a 1% FPR. Paired comparisons across 13 matched pairs give 80% power to detect training on a collection.","solution":"N/A -- no mitigation discussed in source.","labels":["research","privacy"],"sourceUrl":"https://arxiv.org/abs/2610.41732v1","publishedAt":"2026-10-30T13:41:56.000Z","cveId":null,"cweIds":null,"cvssScore":null,"cvssSeverity":null,"severity":"info","attackType":["membership_inference"],"issueType":"research","affectedPackages":null,"affectedPackageNames":null,"affectedPackageRefs":null,"affectedVendors":["Meta"],"affectedVendorsRaw":["OLMo 2 1B"],"classifierModel":"claude-haiku-5-5","classifierPromptVersion":"v4","summaryPromptVersion":"v2","headline":null,"headlinePromptVersion":null,"cvssVector":null,"attackVector":null,"attackComplexity":null,"privilegesRequired":null,"userInteraction":null,"exploitMaturity":null,"epssScore":null,"epssCheckedAt":null,"kevDateAdded":null,"advisoryAliases":null,"affectedPackagesSource":null,"affectedPackagesCheckedAt":null,"patchAvailable":null,"disclosureDate":"2026-10-30T13:41:56.000Z","fixReleasedAt":null,"daysToFix":null,"fixCheckedAt":null,"capecIds":null,"crossRefCount":0,"attackSophistication":"advanced","impactType":["confidentiality"],"aiComponentTargeted":"training_data","llmSpecific":true,"classifierConfidence":0.95,"researchCategory":"preprint","atlasIds":["AML.T0024.000"]}}