In the Linux kernel, the following vulnerability has been resolved:
drm/cirrus-qemu: Validate BAR0 size during probe
The cirrus-qemu driver relies on CIRRUS_VRAM_SIZE (4 MB) to validate
framebuffer sizes. However, during PCI probe, the driver mapped BAR0
without verifying that its size matches CIRRUS_VRAM_SIZE.
If a PCI device with a BAR0 smaller than 4 MB is bound to the driver, the
mapped VRAM will be smaller than expected. Because validation checks assume
4 MB VRAM, framebuffers larger than the mapped memory can be created.
When the display plane is updated (e.g. during release),
cirrus_primary_plane_helper_atomic_update() copies the framebuffer to
VRAM using drm_fb_memcpy(). Writing past the end of the mapped I/O memory
causes a supervisor write page fault:
BUG: unable to handle page fault for address: ffffc9000389c000
...
RIP: 0010:memcpy_toio+0x7c/0xe0 arch/x86/lib/iomem.c:110
...
Call Trace:
iosys_map_memcpy_to include/linux/iosys-map.h:285 [inline]
drm_fb_memcpy+0x325/0x5d0 drivers/gpu/drm/drm_format_helper.c:442
cirrus_primary_plane_helper_atomic_update+0x98a/0xb00
drivers/gpu/drm/tiny/cirrus-qemu.c:358
drm_atomic_helper_commit_planes+0x626/0xea0
drivers/gpu/drm/drm_atomic_helper.c:3038
drm_atomic_helper_commit_tail+0x60/0x510
drivers/gpu/drm/drm_atomic_helper.c:1989
commit_tail+0x2b1/0x3c0 drivers/gpu/drm/drm_atomic_helper.c:2074
drm_atomic_helper_commit+0xa77/0xb10
drivers/gpu/drm/drm_atomic_helper.c:2312
Fix this by validating in cirrus_pci_probe() that the PCI BAR0 resource
is not less than CIRRUS_VRAM_SIZE, returning -ENODEV if it is less.
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.NVD CVSS v3 · CVSS v3.0 or v3.1
- EG Likelihood
- 0.1% within 30 daysSource: FIRST EPSS. 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