In the Linux kernel, the following vulnerability has been resolved:
tcp: fix page frag corruption on page fault
Steffen reported a TCP stream corruption for HTTP requests
served by the apache web-server using a cifs mount-point
and memory mapping the relevant file.
The root cause is quite similar to the one addressed by
commit 20eb4f29b602 ("net: fix sk_page_frag() recursion from
memory reclaim"). Here the nested access to the task page frag
is caused by a page fault on the (mmapped) user-space memory
buffer coming from the cifs file.
The page fault handler performs an smb transaction on a different
socket, inside the same process context. Since sk->sk_allaction
for such socket does not prevent the usage for the task_frag,
the nested allocation modify "under the hood" the page frag
in use by the outer sendmsg call, corrupting the stream.
The overall relevant stack trace looks like the following:
httpd 78268 [001] 3461630.850950: probe:tcp_sendmsg_locked:
ffffffff91461d91 tcp_sendmsg_locked+0x1
ffffffff91462b57 tcp_sendmsg+0x27
ffffffff9139814e sock_sendmsg+0x3e
ffffffffc06dfe1d smb_send_kvec+0x28
[...]
ffffffffc06cfaf8 cifs_readpages+0x213
ffffffff90e83c4b read_pages+0x6b
ffffffff90e83f31 __do_page_cache_readahead+0x1c1
ffffffff90e79e98 filemap_fault+0x788
ffffffff90eb0458 __do_fault+0x38
ffffffff90eb5280 do_fault+0x1a0
ffffffff90eb7c84 __handle_mm_fault+0x4d4
ffffffff90eb8093 handle_mm_fault+0xc3
ffffffff90c74f6d __do_page_fault+0x1ed
ffffffff90c75277 do_page_fault+0x37
ffffffff9160111e page_fault+0x1e
ffffffff9109e7b5 copyin+0x25
ffffffff9109eb40 _copy_from_iter_full+0xe0
ffffffff91462370 tcp_sendmsg_locked+0x5e0
ffffffff91462370 tcp_sendmsg_locked+0x5e0
ffffffff91462b57 tcp_sendmsg+0x27
ffffffff9139815c sock_sendmsg+0x4c
ffffffff913981f7 sock_write_iter+0x97
ffffffff90f2cc56 do_iter_readv_writev+0x156
ffffffff90f2dff0 do_iter_write+0x80
ffffffff90f2e1c3 vfs_writev+0xa3
ffffffff90f2e27c do_writev+0x5c
ffffffff90c042bb do_syscall_64+0x5b
ffffffff916000ad entry_SYSCALL_64_after_hwframe+0x65
The cifs filesystem rightfully sets sk_allocations to GFP_NOFS,
we can avoid the nesting using the sk page frag for allocation
lacking the __GFP_FS flag. Do not define an additional mm-helper
for that, as this is strictly tied to the sk page frag usage.
v1 -> v2:
- use a stricted sk_page_frag() check instead of reordering the
code (Eric)
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.9): severity, escalated by confirmed exploitation. This CVE's 5.9 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.9 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
- 0.9% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-25). 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, and whom BOD 26-04 binds: 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.
The score's inputs: 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