# CWE-121: Stack-based Buffer Overflow

**Likelihood of exploit:** High · **KEV-linked**

> As of 2026-10-05, CWE-121 (Stack-based Buffer Overflow) underlies 28 CVEs tracked by Threadlinqs, 3 of them in the CISA Known Exploited Vulnerabilities catalog, and is cited by 39 tracked threats. MITRE rates its likelihood of exploit as High.

**Last updated:** 2026-10-05

## What is CWE-121?

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

CWE-121 is a variant-level weakness in MITRE’s Common Weakness Enumeration, with a MITRE likelihood of exploit of High. Applicable platforms: Language: Memory-Unsafe; Language: C; Language: C++; Technology: Not Technology-Specific.

_Source: [MITRE CWE](https://cwe.mitre.org/data/definitions/121.html) (CWE-121 definition, reproduced verbatim). Counts and linkage below are Threadlinqs data._

## Consequences

- **Availability** — Modify Memory, DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory). Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
- **Integrity, Confidentiality, Availability, Access Control** — Modify Memory, Execute Unauthorized Code or Commands, Bypass Protection Mechanism. Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.
- **Integrity, Confidentiality, Availability, Access Control, Other** — Modify Memory, Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Other. When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

_Source: MITRE CWE, common consequences._

## How CWE-121 is exploited in the wild

Threadlinqs maps 28 CVEs to CWE-121, published between 2025-01-08 and 2026-09-29. 3 are listed in CISA’s Known Exploited Vulnerabilities catalog, the authoritative record of exploitation in the wild, and 1 is tied to ransomware campaigns. By CVSS v3 severity the set splits into 14 critical, 8 high, 3 medium, 1 low. The highest EPSS score in the set is 94.1% (CVE-2025-0282), the modelled probability of exploitation in the next 30 days. 39 tracked threats reference CWE-121 directly or through a CVE it covers; the most recent is “Fortra Patches Critical Vulnerabilities in BoKS Privileged Access Manager (CVE-2026-79901, CVE-2026-79898, CVE-2026-12627)” (2026-10-03). Affected products concentrate in QNAP Systems Inc. (5), D-Link (2), Microsoft (2), among 19 vendors in total.

## Vulnerabilities (CVEs)

All 28 CVEs mapped to CWE-121, CISA KEV first, then by CVSS score.

- [CVE-2025-53521](https://intel.threadlinqs.com/cve/CVE-2025-53521) — CISA KEV · CVSS 9.8 critical · EPSS 41.4% · published 2025-10-15
- [CVE-2025-0282](https://intel.threadlinqs.com/cve/CVE-2025-0282) — CISA KEV · CVSS 9 critical · EPSS 94.1% · published 2025-01-08
- [CVE-2026-7273](https://intel.threadlinqs.com/cve/CVE-2026-7273) — CISA KEV · CVSS 8.8 high · EPSS 0.3% · published 2026-06-16
- [CVE-2026-94089](https://intel.threadlinqs.com/cve/CVE-2026-94089) — CVSS 10 critical · EPSS 0.9% · published 2026-09-20
- [CVE-2026-79911](https://intel.threadlinqs.com/cve/CVE-2026-79911) — CVSS 10 critical · EPSS 0.6% · published 2026-08-25
- [CVE-2026-82592](https://intel.threadlinqs.com/cve/CVE-2026-82592) — CVSS 9.9 critical · EPSS 0.7% · published 2026-08-30
- [CVE-2026-19959](https://intel.threadlinqs.com/cve/CVE-2026-19959) — CVSS 9.9 critical · EPSS 0.4% · published 2026-08-16
- [CVE-2026-51807](https://intel.threadlinqs.com/cve/CVE-2026-51807) — CVSS 9.8 critical · EPSS 0.2% · published 2026-07-14
- [CVE-2026-41089](https://intel.threadlinqs.com/cve/CVE-2026-41089) — CVSS 9.8 critical · EPSS 0.1% · published 2026-05-12
- [CVE-2026-90558](https://intel.threadlinqs.com/cve/CVE-2026-90558) — CVSS 9.8 critical · published 2026-09-12
- [CVE-2026-91843](https://intel.threadlinqs.com/cve/CVE-2026-91843) — CVSS 9.8 critical · published 2026-09-16
- [CVE-2026-33826](https://intel.threadlinqs.com/cve/CVE-2026-33826) — CVSS 9.1 critical · EPSS 1.0% · published 2026-04-14
- [CVE-2026-26240](https://intel.threadlinqs.com/cve/CVE-2026-26240) — CVSS 9.1 critical · EPSS 0.3% · published 2026-06-10
- [CVE-2026-26241](https://intel.threadlinqs.com/cve/CVE-2026-26241) — CVSS 9.1 critical · EPSS 0.3% · published 2026-06-10
- [CVE-2025-68670](https://intel.threadlinqs.com/cve/CVE-2025-68670) — CVSS 9.1 critical · EPSS 0.2% · published 2026-01-27
- [CVE-2026-4747](https://intel.threadlinqs.com/cve/CVE-2026-4747) — CVSS 8.8 high · EPSS 1.9% · published 2026-03-26
- [CVE-2026-26239](https://intel.threadlinqs.com/cve/CVE-2026-26239) — CVSS 8.1 high · EPSS 0.2% · published 2026-06-10
- [CVE-2026-86093](https://intel.threadlinqs.com/cve/CVE-2026-86093) — CVSS 7.5 high · EPSS 0.4% · published 2026-09-10
- [CVE-2026-88388](https://intel.threadlinqs.com/cve/CVE-2026-88388) — CVSS 7.5 high · EPSS 0.3% · published 2026-09-24
- [CVE-2026-67866](https://intel.threadlinqs.com/cve/CVE-2026-67866) — CVSS 7.5 high · EPSS 0.2% · published 2026-08-05
- [CVE-2023-20577](https://intel.threadlinqs.com/cve/CVE-2023-20577) — CVSS 7.4 high · EPSS 0.1% · published 2026-09-02
- [CVE-2025-66280](https://intel.threadlinqs.com/cve/CVE-2025-66280) — CVSS 7.2 high · EPSS 0.3% · published 2026-06-10
- [CVE-2025-62858](https://intel.threadlinqs.com/cve/CVE-2025-62858) — CVSS 6.5 medium · EPSS 0.3% · published 2026-06-09
- [CVE-2026-68516](https://intel.threadlinqs.com/cve/CVE-2026-68516) — CVSS 6.5 medium · published 2026-08-24
- [CVE-2026-96676](https://intel.threadlinqs.com/cve/CVE-2026-96676) — CVSS 6.3 medium · EPSS 0.2% · published 2026-09-23
- [CVE-2026-21807](https://intel.threadlinqs.com/cve/CVE-2026-21807) — CVSS 3.9 low · EPSS 0.0% · published 2026-08-26
- [CVE-2026-18145](https://intel.threadlinqs.com/cve/CVE-2026-18145) — EPSS 0.3% · published 2026-09-29
- [CVE-2026-7260](https://intel.threadlinqs.com/cve/CVE-2026-7260) — EPSS 0.1% · published 2026-07-30

## Affected vendors

- **QNAP Systems Inc.** — 5 CVEs
- [D-Link](https://intel.threadlinqs.com/vendors/d-link) — 2 CVEs
- [Microsoft](https://intel.threadlinqs.com/vendors/microsoft) — 2 CVEs
- **AMD** — 1 CVE
- **AcademySoftwareFoundation** — 1 CVE
- **Edimax** — 1 CVE
- [F5](https://intel.threadlinqs.com/vendors/f5) — 1 CVE
- **Fast** — 1 CVE
- [FreeBSD](https://intel.threadlinqs.com/vendors/freebsd) — 1 CVE
- **HCLSoftware** — 1 CVE
- [IBM](https://intel.threadlinqs.com/vendors/ibm) — 1 CVE
- [Ivanti](https://intel.threadlinqs.com/vendors/ivanti) — 1 CVE

## Threat activity

39 tracked threats cite CWE-121; the 25 most recent are listed.

- [Fortra Patches Critical Vulnerabilities in BoKS Privileged Access Manager (CVE-2026-79901, CVE-2026-79898, CVE-2026-12627)](https://intel.threadlinqs.com/threat/TL-2026-2854) — CRITICAL · 2026-10-03
- [Multiple Vulnerabilities in Microsoft Edge prior to 154.0.4258.53 (HK GovCERT A26-10-03)](https://intel.threadlinqs.com/threat/TL-2026-2838) — CRITICAL · 2026-10-02
- [WatchGuard Fireware OS Critical Code Injection Vulnerability in BOVPN over TLS Client (CVE-2026-86131)](https://intel.threadlinqs.com/threat/TL-2026-2813) — CRITICAL · 2026-09-30
- [Eclypsium InfraTrust Report: Mass Active Exploitation of Network Management Systems (Cisco FMC/ISE CVE-2026-20079, CVE-2026-76460; SonicWall SMA 1000 CVE-2026-83548/83549; Linux Kernel CopyFail CVE-2026-31431)](https://intel.threadlinqs.com/threat/TL-2026-2630) — CRITICAL · 2026-09-23
- [Chinese-Speaking 'Kapibala' Actor (Red Heron-Linked) Chains WordPress wp2shell, Zyxel GS1900, and Ubiquiti UniFi OS Flaws to Steal Government Data](https://intel.threadlinqs.com/threat/TL-2026-2619) — CRITICAL · 2026-09-22
- [Zyxel GS1900 Series Switches Stack-Based Buffer Overflow (CVE-2026-7273) Actively Exploited by Kapibala/Red Heron in Global 996-Device Campaign — Added to CISA KEV](https://intel.threadlinqs.com/threat/TL-2026-2611) — CRITICAL · 2026-09-21
- [Critical Check Point Management Server Flaw (CVE-2026-91843) Lets Unauthenticated Attackers Run Code as Root](https://intel.threadlinqs.com/threat/TL-2026-2557) — CRITICAL · 2026-09-18
- [Multiple Vulnerabilities in Fortigate NGFW on RUGGEDCOM APE1808 Devices (SSA-864900) — Including Actively Exploited FortiCloud SSO Bypass (CVE-2025-59718/-59719) and FortiOS Heap Overflow (CVE-2025-25249)](https://intel.threadlinqs.com/threat/TL-2026-2486) — CRITICAL · 2026-09-13
- [September 2026 Microsoft Patch Tuesday — Record 966+ Vulnerabilities with Two Actively Exploited Zero-Days (CVE-2026-81963, CVE-2026-85880) and Multiple Critical Wormable RCEs](https://intel.threadlinqs.com/threat/TL-2026-2398) — CRITICAL · 2026-09-08
- [Microsoft September 2026 Patch Tuesday — 999 CVEs, 3 actively exploited zero-days (CVE-2026-85880, CVE-2026-81963, CVE-2026-85046)](https://intel.threadlinqs.com/threat/TL-2026-2407) — CRITICAL · 2026-09-08
- [Broadcom Patches Critical VMware Workstation and Fusion VM Escape Vulnerabilities (CVE-2026-59346, CVE-2026-59347)](https://intel.threadlinqs.com/threat/TL-2026-2340) — CRITICAL · 2026-09-05
- [Adobe and Nvidia Patch Dozens of Vulnerabilities Across Multiple Products, Including Two Critical Flaws in Nvidia's NemoClaw AI Agent Stack and a CVSS 10.0 Adobe Campaign Classic Chain](https://intel.threadlinqs.com/threat/TL-2026-2152) — CRITICAL · 2026-08-26
- [Microsoft August 2026 Patch Tuesday: 400 Flaws Fixed, Including Lazarus-Exploited Zero-Day CVE-2026-68820 (AFD.sys) and Two Publicly Disclosed Zero-Days (CVE-2026-62832 "LegacyHive", CVE-2026-72971)](https://intel.threadlinqs.com/threat/TL-2026-1987) — CRITICAL · 2026-08-11
- [Multiple Vulnerabilities in PHP (GovCERT.HK A26-07-52): Phar Symlink DoS, Bundled-libgd GIF Memory Corruption, pgsql SQL Injection, and BCMath Out-of-Bounds Write (CVE-2026-7260, CVE-2026-9672, CVE-2026-17543, CVE-2026-17544)](https://intel.threadlinqs.com/threat/TL-2026-1782) — HIGH · 2026-07-31
- [Sen. Wyden Urges Binding Federal Mandate to Purge Internet-Facing Legacy VPNs for Zero-Trust Remote Access](https://intel.threadlinqs.com/threat/TL-2026-1774) — MEDIUM · 2026-07-27
- [Google Chrome 150.0.7871.181/.182 Patches 12 High-Severity Vulnerabilities (CVE-2026-16413 through CVE-2026-16424)](https://intel.threadlinqs.com/threat/TL-2026-1605) — HIGH · 2026-07-22
- [CVE-2025-62507: Unauthenticated Stack-Based Buffer Overflow RCE in Redis XACKDEL Command](https://intel.threadlinqs.com/threat/TL-2026-1537) — HIGH · 2026-07-19
- [Pre-Auth Remote Code Execution in Enterprise Network Printer Firmware via Fuzzed Management Protocol (STAR Labs Research)](https://intel.threadlinqs.com/threat/TL-2026-1542) — HIGH · 2026-07-19
- [Multiple Notepad++ Vulnerabilities Enable PowerShell Command Injection, Stack Buffer Overflow, and Zip Slip Path Traversal (CVE-2026-52886, CVE-2026-54758, CVE-2026-57233)](https://intel.threadlinqs.com/threat/TL-2026-1348) — MEDIUM · 2026-07-15
- [Claude Mythos / Project Glasswing: Autonomous AI Vulnerability Discovery Compresses the Find-to-Exploit Timeline (CVE-2026-4747 and the AI-Scale Disclosure Problem)](https://intel.threadlinqs.com/threat/TL-2026-1253) — HIGH · 2026-07-13
- [CVE-2008-4128 Cisco IOS CSRF Vulnerability Added to CISA KEV — Exploited by Russian FSB Center 16 (Static Tundra / Berserk Bear) in Ongoing Router-Hygiene Espionage Campaign](https://intel.threadlinqs.com/threat/TL-2026-1272) — HIGH · 2026-07-13
- [Microsoft's MDASH AI Scanning Harness Uncovers 16 Windows CVEs, Including Four Critical RCE Flaws in TCP/IP, IKEv2, Netlogon, and DNS](https://intel.threadlinqs.com/threat/TL-2026-1184) — CRITICAL · 2026-07-10
- [Multiple WolfSSL Critical Vulnerabilities: Certificate Bypass, RCE, and Post-Quantum Weakening](https://intel.threadlinqs.com/threat/TL-2026-1008) — CRITICAL · 2026-06-30
- [QNAP QSA-26-10: Multiple Injection and Memory-Safety Vulnerabilities in QTS, QuTS hero, QuTS cloud, QVP, and File Station (CVE-2025-66273, CVE-2026-26240, and 12 others)](https://intel.threadlinqs.com/threat/TL-2026-0901) — HIGH · 2026-06-22
- [AryStinger (Ary-Attack) Botnet Compromises 4,000+ Legacy D-Link/RTL819X Routers and NAS for Global Attack Proxy Infrastructure (CVE-2013-3307, CVE-2016-5681, CVE-2025-11837)](https://intel.threadlinqs.com/threat/TL-2026-0894) — HIGH · 2026-06-21

## Mitigations

- **Operation, Build and Compilation / Environment Hardening**: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
- **Architecture and Design**: Use an abstraction library to abstract away risky APIs. Not a complete solution.
- **Implementation**: Implement and perform bounds checking on input.
- **Implementation**: Do not use dangerous functions such as gets. Use safer, equivalent functions which check for boundary errors.
- **Operation, Build and Compilation / Environment Hardening**: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would…

_Source: MITRE CWE, potential mitigations._

## Detection methods (MITRE CWE)

- **Fuzzing** (effectiveness: High): Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.
- **Automated Static Analysis** (effectiveness: High): Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
- **Automated Dynamic Analysis** (effectiveness: Moderate): Use tools that are integrated during compilation to insert runtime error-checking mechanisms related to memory safety errors, such as AddressSanitizer (ASan) for C/C++ [REF-1518].

_Source: MITRE CWE, detection methods. Threadlinqs detection rules for the threats above are Blue tier and higher._

## Related weaknesses

- [CWE-788](https://cwe.mitre.org/data/definitions/788.html)
- [CWE-787 Out-of-bounds Write](https://intel.threadlinqs.com/cwe/CWE-787)

Canonical: https://intel.threadlinqs.com/cwe/CWE-121
Source definition: https://cwe.mitre.org/data/definitions/121.html
Detection rules and IOCs for threats exploiting CWE-121 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp