In the Linux kernel, the following vulnerability has been resolved:
virtio_net: Fix misalignment bug in struct virtnet_info
Use the new TRAILING_OVERLAP() helper to fix a misalignment bug
along with the following warning:
drivers/net/virtio_net.c:429:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it (in this case
u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];). This
overlays the trailing members (rss_hash_key_data) onto the FAM
(hash_key_data) while keeping the FAM and the start of MEMBERS aligned.
The static_assert() ensures this alignment remains.
Notice that due to tail padding in flexible struct
virtio_net_rss_config_trailer, rss_trailer.hash_key_data
(at offset 83 in struct virtnet_info) and rss_hash_key_data (at
offset 84 in struct virtnet_info) are misaligned by one byte. See
below:
struct virtio_net_rss_config_trailer {
__le16 max_tx_vq; /* 0 2 */
__u8 hash_key_length; /* 2 1 */
__u8 hash_key_data[]; /* 3 0 */
/* size: 4, cachelines: 1, members: 3 */
/* padding: 1 */
/* last cacheline: 4 bytes */
};
struct virtnet_info {
...
struct virtio_net_rss_config_trailer rss_trailer; /* 80 4 */
/* XXX last struct has 1 byte of padding */
u8 rss_hash_key_data[40]; /* 84 40 */
...
/* size: 832, cachelines: 13, members: 48 */
/* sum members: 801, holes: 8, sum holes: 31 */
/* paddings: 2, sum paddings: 5 */
};
After changes, those members are correctly aligned at offset 795:
struct virtnet_info {
...
union {
struct virtio_net_rss_config_trailer rss_trailer; /* 792 4 */
struct {
unsigned char __offset_to_hash_key_data[3]; /* 792 3 */
u8 rss_hash_key_data[40]; /* 795 40 */
}; /* 792 43 */
}; /* 792 44 */
...
/* size: 840, cachelines: 14, members: 47 */
/* sum members: 801, holes: 8, sum holes: 35 */
/* padding: 4 */
/* paddings: 1, sum paddings: 4 */
/* last cacheline: 8 bytes */
};
As a result, the RSS key passed to the device is shifted by 1
byte: the last byte is cut off, and instead a (possibly
uninitialized) byte is added at the beginning.
As a last note struct virtio_net_rss_config_hdr *rss_hdr; is also
moved to the end, since it seems those three members should stick
around together. :)
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. 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