AI 中文总结
本文针对数据库后过滤访问控制的侧信道，利用丰富查询接口将存在性泄漏放大为重建攻击，在PostgreSQL和Elasticsearch/OpenSearch场景下实现高熵记录的高效恢复，凸显FGAC侧信道评估需考虑丰富谓词的必要性。
AI 中文摘要
细粒度访问控制（FGAC）机制，如行级安全（RLS）和文档级安全（DLS），被广泛部署在数据库中，以限制多个用户共享的物理索引结构中存储的数据访问（例如多租户数据库，或组织内最小权限的实现）。FGAC实现常采用后过滤方式，即不可信查询在所有数据上运行，之后对私有结果进行编辑。现有研究表明，该方法会产生侧信道，使攻击者能测试选定值是否存在于未查看的数据中。尽管存在危害，但现有攻击无法高效恢复高熵的丰富数据，如完整记录或文本文档。本文表明这些侧信道的危害比此前认为的更大：利用丰富的查询接口（如范围、前缀和合取谓词），可将存在性泄漏放大为重建攻击，具体在两种场景下实现：1. PostgreSQL（RLS时序）：利用时序侧信道和表达性SQL查询（如范围、合取），通过对大域进行二分法搜索枚举未知属性值，进而恢复完整记录；2. Elasticsearch/OpenSearch（DLS评分）：利用评分和前缀扩展侧信道恢复文档中的索引词，部分情况下可提取语料库中的n元语法以恢复近似文本。研究结果表明，FGAC侧信道需在存在丰富谓词的情况下进行评估，此类谓词可将成员测试转化为高熵记录的可扩展重建。
英文摘要
Fine-grained access control (FGAC) mechanisms such as row-level security (RLS) and document-level security (DLS) are widely deployed in databases to restrict access to data stored in physical indexing structures shared by multiple users (e.g., in multi-tenant databases, or in the implementation of least-privilege within an organization). FGAC implementations often use post-filtering where untrusted queries run over all data and private results are redacted afterwards. Prior work shows this approach can lead to side-channels that enable attackers to test if a chosen value exists in unseen data. While damaging, prior attacks do not enable the efficient recovery of rich, high-entropy data like full records or text documents. We show these side-channels are more damaging than previously thought. Using rich query interfaces (e.g., range, prefix, and conjunctive predicates), we amplify existence leakage into reconstruction attacks. We do this in two settings: - PostgreSQL (RLS timing). We exploit a timing side-channel and expressive SQL queries (e.g., ranges, conjunctions) to enumerate unknown attribute values and, in turn, full records via binary search over large domains. - Elasticsearch/OpenSearch (DLS scoring). We exploit scoring and prefix-expansion side-channels to recover indexed terms from documents. In some cases, we can extract $n$-grams in the corpus to recover approximate text. Our results show that FGAC side-channels must be evaluated in the presence of rich predicates, which can turn membership tests into scalable reconstruction of high-entropy records.
Comments21 pages, 5 figures, 6 tables. Full version of https://www.usenix.org/conference/usenixsecurity26/presentation/espiritu
Journal refProceedings of the 35th USENIX Security Symposium (2026), 3753-3772
