CVE-2021-22555 | Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE

Exp

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

Published: 2021-07-07 Last update: 2025-10-27 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-22555 is rated Critical Active Threat (91.9/100): CVSS High severity, with high exploitation likelihood (EPSS 85.24%, 99th percentile). CISA KEV confirms active exploitation (added 2025-10-06) affecting Linux / Kernel. a weakness (CWE-787) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2021-22555

Name: Linux Kernel Heap Out-of-Bounds Write Vulnerability · CISA KEV detail

Exploit added: 2025-10-06

Action due: 2025-10-27

Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Public exploit references (Exploit-DB) for CVE-2021-22555

EDB-ID Source Kind Published Link
50135 exploit_db edb 2021-07-15 Exploit-DB ↗
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Exploit prediction scoring system (EPSS) score for CVE-2021-22555

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-28 86.30% 85.24% -1.06%
2 2026-05-26 86.89% 86.30% -0.59%
3 2026-05-22 — 86.89% —

Full EPSS history (57 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-22555

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.3 3.1 HIGH
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.6 6.0 [email protected]
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]
4.6 2.0 MEDIUM
AV:L/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 3.9 6.4 [email protected]

Weakness enumeration for CVE-2021-22555

OS Trackers for CVE-2021-22555

vendor priority summary link
debian not yet assigned CVE-2021-22555 not yet assigned priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-22555
redhat high — https://access.redhat.com/security/cve/CVE-2021-22555
suse high — https://www.suse.com/security/cve/CVE-2021-22555/
ubuntu high CVE-2021-22555 high priority: Ubuntu including 168 source packages (linux, linux-allwinner, …), 2165 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1681, not-affected 224, released 219, ignored 41. https://ubuntu.com/security/CVE-2021-22555

Affected software / configurations for CVE-2021-22555

Vendor Product Version Raw CPE
netapp c400_firmware — cpe:2.3:o:netapp:c400_firmware:-:*:*:*:*:*:*:*
netapp c250_firmware — cpe:2.3:o:netapp:c250_firmware:-:*:*:*:*:*:*:*
netapp h410c_firmware — cpe:2.3:o:netapp:h410c_firmware:-:*:*:*:*:*:*:*
netapp h300s_firmware — cpe:2.3:o:netapp:h300s_firmware:-:*:*:*:*:*:*:*
netapp h500s_firmware — cpe:2.3:o:netapp:h500s_firmware:-:*:*:*:*:*:*:*
netapp h700s_firmware — cpe:2.3:o:netapp:h700s_firmware:-:*:*:*:*:*:*:*
netapp h410s_firmware — cpe:2.3:o:netapp:h410s_firmware:-:*:*:*:*:*:*:*
linux linux_kernel >= 2.6.19, < 4.4.267 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.5, < 4.9.267 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.10, < 4.14.231 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.15, < 4.19.188 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.20, < 5.4.113 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.5, < 5.10.31 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.12 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
brocade fabric_operating_system — cpe:2.3:o:brocade:fabric_operating_system:-:*:*:*:*:*:*:*
netapp fas_8300_firmware — cpe:2.3:o:netapp:fas_8300_firmware:-:*:*:*:*:*:*:*
netapp fas_8700_firmware — cpe:2.3:o:netapp:fas_8700_firmware:-:*:*:*:*:*:*:*
netapp aff_a400_firmware — cpe:2.3:o:netapp:aff_a400_firmware:-:*:*:*:*:*:*:*
netapp aff_a250_firmware — cpe:2.3:o:netapp:aff_a250_firmware:-:*:*:*:*:*:*:*
netapp aff_500f_firmware — cpe:2.3:o:netapp:aff_500f_firmware:-:*:*:*:*:*:*:*
netapp h610c_firmware — cpe:2.3:o:netapp:h610c_firmware:-:*:*:*:*:*:*:*
netapp h610s_firmware — cpe:2.3:o:netapp:h610s_firmware:-:*:*:*:*:*:*:*
netapp h615c_firmware — cpe:2.3:o:netapp:h615c_firmware:-:*:*:*:*:*:*:*
netapp cloud_backup — cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*
netapp hci_management_node — cpe:2.3:a:netapp:hci_management_node:-:*:*:*:*:*:*:*
netapp solidfire — cpe:2.3:a:netapp:solidfire:-:*:*:*:*:*:*:*
netapp solidfire_baseboard_management_controller — cpe:2.3:a:netapp:solidfire_baseboard_management_controller:*:*:*:*:*:*:*:*

References for CVE-2021-22555

URL Tags
http://packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Escalation.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html Exploit Third Party Advisory VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21 Mailing List Patch Vendor Advisory
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d Mailing List Patch Vendor Advisory
https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528 Exploit Third Party Advisory
https://security.netapp.com/advisory/ntap-20210805-0010/ Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22555 US Government Resource
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