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CVE-2026-87121

Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application

9.3 CriticalFix available

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.78%Unchanged since Sep 23, 2026
90%50%10%1%

What each source reports

CVE List Score used 9.3

Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
CVE-2026-87121
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
EUVDEUVD-2026-84816 9.3

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
EUVD-2026-84816
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-h8q6-7rjx-3m2r 9.3

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to...

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
GHSA-h8q6-7rjx-3m2r
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
NVD 9.3

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
CVE-2026-87121
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
OSVDEBIAN-CVE-2026-87121 9.3

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
DEBIAN-CVE-2026-87121
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Updated
2026-11-02
OSVUBUNTU-CVE-2026-87121 9.3

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

Record
UBUNTU-CVE-2026-87121
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
lwip
Debian:12
 All versions, plus listed versions
2.1.3+dfsg1-22.1.3+dfsg1-32.1.3+dfsg1-42.2.0+dfsg1-12.2.0+dfsg1-2
Show 17 moreShow less
2.2.0+dfsg1-32.2.0+dfsg1-42.2.0+dfsg1-52.2.0+dfsg1-62.2.0+dfsg1-6.12.2.0+dfsg1-6.1~exp12.2.0+dfsg1-72.2.0+dfsg1-82.2.0+dfsg1-92.2.1+dfsg1-12.2.1+dfsg1-22.2.1+dfsg1-32.2.1+dfsg1-42.2.1+dfsg1-52.2.1+dfsg1-62.2.1+dfsg1-72.2.1+dfsg1-8
 None known
lwip
Debian:13
 All versions, plus listed versions
2.2.1+dfsg1-12.2.1+dfsg1-1+deb13u12.2.1+dfsg1-22.2.1+dfsg1-32.2.1+dfsg1-4
Show 4 moreShow less
2.2.1+dfsg1-52.2.1+dfsg1-62.2.1+dfsg1-72.2.1+dfsg1-8
 None known
lwip
Debian:14
 before 2.2.1+dfsg1-8, plus listed versions
2.2.1+dfsg1-12.2.1+dfsg1-22.2.1+dfsg1-32.2.1+dfsg1-42.2.1+dfsg1-52.2.1+dfsg1-62.2.1+dfsg1-7
2.2.1+dfsg1-8
lwip
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
2.1.2-32.1.2-5.12.1.2+dfsg1-12.1.2+dfsg1-42.1.2+dfsg1-4ubuntu0.1~esm1
 None known
lwip
Ubuntu:Pro:22.04:LTS
 All versions, plus listed versions
2.1.2+dfsg1-82.1.2+dfsg1-92.1.3+dfsg1-12.1.3+dfsg1-1ubuntu0.1~esm1
 None known
lwip
Ubuntu:Pro:24.04:LTS
 All versions, plus listed versions
2.1.3+dfsg1-22.1.3+dfsg1-42.2.0+dfsg1-22.2.0+dfsg1-32.2.0+dfsg1-4
Show 6 moreShow less
2.2.0+dfsg1-52.2.0+dfsg1-62.2.0+dfsg1-6.12.2.0+dfsg1-6.1build12.2.0+dfsg1-6.1build22.2.0+dfsg1-6.1ubuntu0.1~esm1
 None known
lwip
Ubuntu:26.10
 All versions, plus listed versions
2.2.1+dfsg1-42.2.1+dfsg1-52.2.1+dfsg1-7
 None known
lwip
Ubuntu:Pro:26.04:LTS
 All versions, plus listed versions
2.2.1+dfsg1-22.2.1+dfsg1-32.2.1+dfsg1-42.2.1+dfsg1-4ubuntu0.1~esm1
 None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-87121 is a critical vulnerability (CVSS 9.3) in Lwip Tcp/ip Stack Mqtt, published September 22, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.78%, the 55th percentile. Fixed in lwip 2.2.1+dfsg1-8.

References

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