In the Linux kernel, the following vulnerability has been resolved:
x86/bhi: Avoid warning in #DB handler due to BHI mitigation
When BHI mitigation is enabled, if SYSENTER is invoked with the TF flag set
then entry_SYSENTER_compat() uses CLEAR_BRANCH_HISTORY and calls the
clear_bhb_loop() before the TF flag is cleared. This causes the #DB handler
(exc_debug_kernel()) to issue a warning because single-step is used outside the
entry_SYSENTER_compat() function.
To address this issue, entry_SYSENTER_compat() should use CLEAR_BRANCH_HISTORY
after making sure the TF flag is cleared.
The problem can be reproduced with the following sequence:
$ cat sysenter_step.c
int main()
{ asm("pushf; pop %ax; bts $8,%ax; push %ax; popf; sysenter"); }
$ gcc -o sysenter_step sysenter_step.c
$ ./sysenter_step
Segmentation fault (core dumped)
The program is expected to crash, and the #DB handler will issue a warning.
Kernel log:
WARNING: CPU: 27 PID: 7000 at arch/x86/kernel/traps.c:1009 exc_debug_kernel+0xd2/0x160
...
RIP: 0010:exc_debug_kernel+0xd2/0x160
...
Call Trace:
<#DB>
? show_regs+0x68/0x80
? __warn+0x8c/0x140
? exc_debug_kernel+0xd2/0x160
? report_bug+0x175/0x1a0
? handle_bug+0x44/0x90
? exc_invalid_op+0x1c/0x70
? asm_exc_invalid_op+0x1f/0x30
? exc_debug_kernel+0xd2/0x160
exc_debug+0x43/0x50
asm_exc_debug+0x1e/0x40
RIP: 0010:clear_bhb_loop+0x0/0xb0
...
? entry_SYSENTER_compat_after_hwframe+0x6e/0x8d
[ bp: Massage commit message. ]
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.5): severity, escalated by confirmed exploitation. This CVE's 5.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.5 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-17). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it