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NVD / CVE Program· CNA Linux

CVE-2025-38463: tcp: Correct signedness in skb remaining space calculation

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 62e6160cfb5514787bda833d466509edc38fde23, 81373cd1d72d87c7d844d4454a526b8f53e72d00, 9f164fa6bb09fbcc60fa5c3ff551ce9eec1befd7; azl3 kernel 6.6.96.2-2 on Azure Linux 3.0 6.6.104.2-1.
  • Severity is disputed: the assigning authority (CNA) scores it 7.8, NVD 5.5.

Low priority for now. Upgrade to Linux Linux 62e6160cfb5514787bda833d466509edc38fde23, 81373cd1d72d87c7d844d4454a526b8f53e72d00, 9f164fa6bb09fbcc60fa5c3ff551ce9eec1befd7; azl3 kernel 6.6.96.2-2 on Azure Linux 3.0 6.6.104.2-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: tcp: Correct signedness in skb remaining space calculation Syzkaller reported a bug [1] where sk->sk_forward_alloc can overflow. When we send data, if an skb exists at the tail of the write queue, the kernel will attempt to append the new data to that skb. However, the code that checks for available space in the skb is flawed: ''' copy = size_goal - skb->len ''' The types of the variables involved are: ''' copy: ssize_t (s64 on 64-bit systems) size_goal: int skb->len: unsigned int ''' Due to C's type promotion rules, the signed size_goal is converted to an unsigned int to match skb->len before the subtraction. The result is an unsigned int. When this unsigned int result is then assigned to the s64 copy variable, it is zero-extended, preserving its non-negative value. Consequently, copy is always >= 0. Assume we are sending 2GB of data and size_goal has been adjusted to a value smaller than skb->len. The subtraction will result in copy holding a very large positive integer. In the subsequent logic, this large value is used to update sk->sk_forward_alloc, which can easily cause it to overflow. The syzkaller reproducer uses TCP_REPAIR to reliably create this condition. However, this can also occur in real-world scenarios. The tcp_bound_to_half_wnd() function can also reduce size_goal to a small value. This would cause the subsequent tcp_wmem_schedule() to set sk->sk_forward_alloc to a value close to INT_MAX. Further memory allocation requests would then cause sk_forward_alloc to wrap around and become negative. [1]: https://syzkaller.appspot.com/bug?extid=de6565462ab540f50e47

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
Jul 25, 2025
Updated
Aug 5, 2026
EPSS
0.1% · 8th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CNA vs NVD score

NVD
5.5
CNA · Linux
7.8
2.3 point gap

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel6.5 and later · before 6.6.99
  • linux linux kernel6.7 and later · before 6.12.39
  • linux linux kernel6.13 and later · before 6.15.7
  • linux linux kernel6.16

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 6.5affected
    • 270a1c3de47e49dd2fc18f48e46b101e48050e78 and later · before 81373cd1d72d87c7d844d4454a526b8f53e72d00affected · git
    • 270a1c3de47e49dd2fc18f48e46b101e48050e78 and later · before 62e6160cfb5514787bda833d466509edc38fde23affected · git
    • 270a1c3de47e49dd2fc18f48e46b101e48050e78 and later · before 9f164fa6bb09fbcc60fa5c3ff551ce9eec1befd7affected · git
    • 270a1c3de47e49dd2fc18f48e46b101e48050e78 and later · before d3a5f2871adc0c61c61869f37f3e697d97f03d8caffected · git
    • before 6.5not affected · semver
    • 6.6.99 and later · up to and including 6.6.*not affected · semver
    • 6.12.39 and later · up to and including 6.12.*not affected · semver
    • 6.15.7 and later · up to and including 6.15.*not affected · semver
    • 6.16 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10kernel-abi-stablelistsbefore 6.12.0-55.33.1.el10_06.12.0-55.33.1.el10_0
AlmaLinux:10kernel-docbefore 6.12.0-55.33.1.el10_06.12.0-55.33.1.el10_0
Debian:13linuxbefore 6.12.41-16.12.41-1
Debian:14linuxbefore 6.16.3-16.16.3-1
Red Hat:enterprise_linux:10.0kernelbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64kbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-corebefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debugbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-corebefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-debuginfobefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-develbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-devel-matchedbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-modulesbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-modules-corebefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debug-modules-extrabefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-debuginfobefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-develbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-devel-matchedbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-modulesbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-modules-corebefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-64k-modules-extrabefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-abi-stablelistsbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-corebefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0
Red Hat:enterprise_linux:10.0kernel-debugbefore 0:6.12.0-55.33.1.el10_00:6.12.0-55.33.1.el10_0

+71

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-38461Jul 25, 2025 · vsock: Fix transport_* TOCTOU
    18Monitor
  • ← EarlierCVE-2025-38462Jul 25, 2025 · vsock: Fix transport_{g2h,h2g} TOCTOU
    18Monitor
  • Later →CVE-2025-38464Jul 25, 2025 · tipc: Fix use-after-free in tipc_conn_close().
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux62e6160cfb5514787bda833d466509edc38fde23Vendor (CNA)
Linux Linux81373cd1d72d87c7d844d4454a526b8f53e72d00Vendor (CNA)
Linux Linux9f164fa6bb09fbcc60fa5c3ff551ce9eec1befd7Vendor (CNA)
Linux Linuxd3a5f2871adc0c61c61869f37f3e697d97f03d8cVendor (CNA)
azl3 kernel 6.6.96.2-2 on Azure Linux 3.06.6.104.2-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
almalinux:kernel-abi-stablelists6.12.0-55.33.1.el10_0 · AlmaLinux:10Package registry (OSV)
almalinux:kernel-doc6.12.0-55.33.1.el10_0 · AlmaLinux:10Package registry (OSV)
debian:linux6.12.41-1 · Debian:13Package registry (OSV)
red hat:kernel-64k-debug-debuginfo0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-64k-debug-devel0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-64k-debug-devel-matched0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-64k-debuginfo0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-64k-devel0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-64k-devel-matched0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debug-debuginfo0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debug-devel0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debug-devel-matched0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debuginfo0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debuginfo-common-aarch640:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)
red hat:kernel-debuginfo-common-ppc64le0:6.12.0-55.33.1.el10_0 · Red Hat:enterprise_linux:10.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-53176335 days apartIB/isert: Reject login PDUs shorter than ISER_HEADERS_LEN
    39Monitor
  • CVE-2026-63940359 days apartKVM: SEV: Ignore Port I/O requests of length '0'
    37Monitor
  • CVE-2024-26828464 days apartcifs: fix underflow in parse_server_interfaces()
    37Monitor
  • CVE-2026-43187285 days apartxfs: delete attr leaf freemap entries when empty
    35Monitor
  • CVE-2026-53178335 days apartstaging: rtl8723bs: rtw_mlme: add bounds checks before ie_length subtraction
    32Monitor
  • CVE-2024-53061248 days apartmedia: s5p-jpeg: prevent buffer overflows
    31Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-191 · Integer Underflow (Wrap or Wraparound)

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records