In the Linux kernel, the following vulnerability has been resolved:
x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST or Rust >= 1.88
Calling core::fmt::write() from rust code while FineIBT is enabled
results in a kernel panic:
[ 4614.199779] kernel BUG at arch/x86/kernel/cet.c:132!
[ 4614.205343] Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 4614.211781] CPU: 2 UID: 0 PID: 6057 Comm: dmabuf_dump Tainted: G U O 6.12.17-android16-0-g6ab38c534a43 #1 9da040f27673ec3945e23b998a0f8bd64c846599
[ 4614.227832] Tainted: [U]=USER, [O]=OOT_MODULE
[ 4614.241247] RIP: 0010:do_kernel_cp_fault+0xea/0xf0
...
[ 4614.398144] RIP: 0010:_RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x0/0x20
[ 4614.407792] Code: 48 f7 df 48 0f 48 f9 48 89 f2 89 c6 5d e9 18 fd ff ff 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 41 81 ea 14 61 af 2c 74 03 0f 0b 90 <66> 0f 1f 00 55 48 89 e5 48 89 f2 48 8b 3f be 01 00 00 00 5d e9 e7
[ 4614.428775] RSP: 0018:ffffb95acfa4ba68 EFLAGS: 00010246
[ 4614.434609] RAX: 0000000000000000 RBX: 0000000000000010 RCX: 0000000000000000
[ 4614.442587] RDX: 0000000000000007 RSI: ffffb95acfa4ba70 RDI: ffffb95acfa4bc88
[ 4614.450557] RBP: ffffb95acfa4bae0 R08: ffff0a00ffffff05 R09: 0000000000000070
[ 4614.458527] R10: 0000000000000000 R11: ffffffffab67eaf0 R12: ffffb95acfa4bcc8
[ 4614.466493] R13: ffffffffac5d50f0 R14: 0000000000000000 R15: 0000000000000000
[ 4614.474473] ? __cfi__RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x10/0x10
[ 4614.484118] ? _RNvNtCs3o2tGsuHyou_4core3fmt5write+0x1d2/0x250
This happens because core::fmt::write() calls
core::fmt::rt::Argument::fmt(), which currently has CFI disabled:
library/core/src/fmt/rt.rs:
171 // FIXME: Transmuting formatter in new and indirectly branching to/calling
172 // it here is an explicit CFI violation.
173 #[allow(inline_no_sanitize)]
174 #[no_sanitize(cfi, kcfi)]
175 #[inline]
176 pub(super) unsafe fn fmt(&self, f: &mut Formatter<'_>) -> Result {
This causes a Control Protection exception, because FineIBT has sealed
off the original function's endbr64.
This makes rust currently incompatible with FineIBT. Add a Kconfig
dependency that prevents FineIBT from getting turned on by default
if rust is enabled.
[ Rust 1.88.0 (scheduled for 2025-06-26) should have this fixed [1],
and thus we relaxed the condition with Rust >= 1.88.
When objtool lands checking for this with e.g. [2], the plan is
to ideally run that in upstream Rust's CI to prevent regressions
early [3], since we do not control core's source code.
Alice tested the Rust PR backported to an older compiler.
Peter would like that Rust provides a stable core which can be
pulled into the kernel: "Relying on that much out of tree code is
'unfortunate'".
[ Reduced splat. - Miguel ]
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 2026-10-24). 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 low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from 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)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” 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