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CVE-2026-53671: PREVAIL: Context-write no-op in do_mem_store allows unsafe eBPF programs to pass verification

• Severity: critical (CVSS 9.3 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-02 · updated 2026-09-09
• Weakness: CWE-682

Description

PREVAIL is a Polynomial-Runtime EBPF Verifier using an Abstract Interpretation Layer. Prior to version 0.2.4, the abstract transformer in prevail treats writes through a T_CTX-typed base register as a silent no-op: do_mem_store in src/crab/ebpf_transformer.cpp only models T_STACK stores, and the checker's T_CTX bounds arm never tests AccessType::write. An attacker can craft an eBPF program that overwrites a context field (e.g., ctx->data), reload that field typed as T_PACKET, and dereference an attacker-controlled address — and prevail will report the program as safe. This issue has been patched in version 0.2.4.

Affected products

• vbpf prevail: before 0.2.4

References

• https://github.com/vbpf/prevail/commit/de65234f67d2608b54d12571edb585ead224363c
• https://github.com/vbpf/prevail/releases/tag/v0.2.4
• https://github.com/vbpf/prevail/security/advisories/GHSA-65rv-h458-cq99
• https://github.com/vbpf/prevail/security/advisories/GHSA-65rv-h458-cq99

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