netfilter: synproxy: Fix out of bounds when parsing TCP options
Priority LOW 37CWE-125Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- Low · None · High
- Fix status
- Partial Red Hat: 2 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.
Summary
In the Linux kernel, the following vulnerability has been resolved: netfilter: synproxy: Fix out of bounds when parsing TCP options The TCP option parser in synproxy (synproxy_parse_options) could read one byte out of bounds. When the length is 1, the execution flow gets into the loop, reads one byte of the opcode, and if the opcode is neither TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the length of 1. This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack out of bounds when parsing TCP options."). v2 changes: Added an early return when length < 0 to avoid calling skb_header_pointer with negative length.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00784 56th percentileScored 2026-11-07
Fix Partial Linux (Linux): 4.4.274, 4.9.274, 4.14.238 +5Red Hat: 2 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 3.12 and later | 4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.4.128, 5.10.46, 5.12.13, 5.13 | Patch available | CNA |
- Linux VendorLinux Affected 3.12 and later Fixed in 4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.4.128, 5.10.46, 5.12.13, 5.13 Patch available CNA
CPE configurations NVD · 7
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | 3.12 to before 4.4.274; 4.5 to before 4.9.274; 4.10 to before 4.14.238; 4.15 to before 4.19.196; 4.20 to before 5.4.128; 5.5 to before 5.10.46; 5.11 to before 5.12.13 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc1:*:*:*:*:*:* | 5.13 rc1 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc2:*:*:*:*:*:* | 5.13 rc2 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc3:*:*:*:*:*:* | 5.13 rc3 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc4:*:*:*:*:*:* | 5.13 rc4 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc5:*:*:*:*:*:* | 5.13 rc5 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.13:rc6:*:*:*:*:*:* | 5.13 rc6 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions 3.12 to before 4.4.274; 4.5 to before 4.9.274; 4.10 to before 4.14.238; 4.15 to before 4.19.196; 4.20 to before 5.4.128; 5.5 to before 5.10.46; 5.11 to before 5.12.13 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc1:*:*:*:*:*:* Versions 5.13 rc1 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc2:*:*:*:*:*:* Versions 5.13 rc2 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc3:*:*:*:*:*:* Versions 5.13 rc3 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc4:*:*:*:*:*:* Versions 5.13 rc4 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc5:*:*:*:*:*:* Versions 5.13 rc5 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.13:rc6:*:*:*:*:*:* Versions 5.13 rc6 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.4.128, 5.10.46, 5.12.13, 5.13
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
Not affected: 2 products
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-47245
- 2026-10-03 Alias added: GHSA-ch44-784c-7wgq
References
Patch 8
- https://git.kernel.org/stable/c/e1eb98cfeafdd85537e7e3cefe93ca9bfbcc3ea8
- https://git.kernel.org/stable/c/576c1526b4d83c44ad7b673cb841f36cbc6cb6c4
- https://git.kernel.org/stable/c/674b5f0c6a4fc5d3abce877048290cea6091fcb1
- https://git.kernel.org/stable/c/7d9a9a1a88a3da574e019b4de756bc73337b3b0b
- https://git.kernel.org/stable/c/6defc77d48eff74075b80ad5925061b2fc010d98
- https://git.kernel.org/stable/c/9cdf299ba4e153b5e56187648420de22c6216f02
- https://git.kernel.org/stable/c/f648089337cb8ed40b2bb96e244f72b9d97dc96b
- https://git.kernel.org/stable/c/5fc177ab759418c9537433e63301096e733fb915
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- TI-2013-05264 The (1) get_user and (2) put_user API functions in the Linux kernel before 3.5.5 on the… KEVCVSS 3.1HIGH 8.8
- TI-2022-00125 Integer overflow in kernel KEVCVSS 3.1HIGH 8.4
- TI-2013-01864 The perf_swevent_init function in kernel/events/core.c in the Linux kernel before 3.8.9… KEVCVSS 3.1HIGH 8.4
- TI-2021-05514 Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE KEVCVSS 3.1HIGH 8.3
Sources
- CVE-2021-47245 · CVE Program
- CVE-2021-47245 · NVD
- FIRST EPSS
- GHSA-ch44-784c-7wgq · GitHub Advisory Database · CC BY 4.0
- CVE-2021-47245 · Red Hat security data · CC BY 4.0
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