Full Report
Researchers found a way to bypass recent mitigations for Spectre v2 speculative execution side-channel attacks and developed an exploit to leak secrets from Linux machines. [...]
Analysis Summary
# Vulnerability: TONTOU (Time-of-Neutralization to Time-of-Use) Spectre v2 Bypass
## CVE Details
- **CVE ID:** CVE-2026-XXXXX (Specific ID not provided in text; referred to as "Interrupt Injection" or "TONTOU")
- **CVSS Score:** N/A (Not officially scored in article, but addresses a critical bypass of kernel mitigations)
- **CWE:** CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor), CWE-440 (Expected Behavior Violation)
## Affected Systems
- **Products:** Systems utilizing AMD and Intel CPUs.
- **Versions:** Linux Kernel versions (specifically tested on 6.14.0-37-generic).
- **Configurations:** Systems relying on "neutralization-based" Spectre v2 mitigations (e.g., Safe RET, BTI mitigations that sanitize/isolate branch predictors). Specifically affects AMD Zen 2 and potentially newer architectures.
## Vulnerability Description
The TONTOU (Time-of-Neutralization to Time-of-Use) attack exploits a race condition window between the moment a processor sanitizes/isolates its branch predictor state (Neutralization) and the moment the victim branch is executed.
By using **Interrupt Injection**, an unprivileged attacker can schedule timer interrupts to trigger precisely within this window during kernel execution. When the kernel is redirected to the interrupt handler, the attacker can "re-poison" the branch predictor or Return Stack Buffer (RSB). This causes the CPU to speculatively execute code at an attacker-chosen location despite existing mitigations, leaking sensitive data via side channels.
## Exploitation
- **Status:** PoC available (demonstrated by MIT CSAIL researchers).
- **Complexity:** High (requires precise interrupt timing and alignment).
- **Attack Vector:** Local (requires the ability to run unprivileged code on the target machine).
## Impact
- **Confidentiality:** **High.** Demonstrated ability to leak arbitrary kernel memory, including `/etc/shadow` password hashes, at a rate of 5.47 bytes/s.
- **Integrity:** None.
- **Availability:** None.
## Remediation
### Patches
- **Linux Kernel:** Formal patches for version 6.14 and others are pending/in development following the disclosure at Black Hat USA 2026.
- **AMD:** Has acknowledged the issue, noting it relates to the Linux implementation of the **Safe RET** mitigation.
### Workarounds
- Monitor for unusual timer interrupt frequencies from unprivileged processes.
- Disable unprivileged access to high-precision timers where possible (though this may impact system performance).
## Detection
- **Indicators of Compromise:** High frequency of timer interrupts triggered by a single unprivileged process.
- **Detection methods and tools:** Performance monitoring tools (e.g., `perf`) can be used to detect anomalies in branch mispredictions and interrupt rates.
## References
- MIT CSAIL Research Paper: hxxps[://]people[.]csail[.]mit[.]edu/mengjia/data/2026[.]USENIX[.]TONTOU[.]pdf
- Black Hat USA 2026 Briefing: hxxps[://]blackhat[.]com/us-26/briefings/schedule/#breaking-recently-deployed-spectre-v2-mitigations-a-novel-attack-primitive-53157
- Related Vulnerability (Inception): hxxps[://]www[.]bleepingcomputer[.]com/news/security/new-inception-attack-leaks-sensitive-data-from-all-amd-zen-cpus/