Cyber Resilience

CVE-2020-3118

Memory Safety in Cisco Ios Xr 6.6.0 – 6.6.12

CISA KEVActive ExploitationEUVD ExploitedPublic PoCMemory Safety
Published
05 February 2020
Modified
28 October 2025
KEV Added
03 November 2021
Patch / advisory
View advisory
CVSS Score v3.1 8.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.12 96th percentile
Risk Priority 90 floored blend · peak EPSS

Summary

CVE-2020-3118 is a high-severity Use of Externally-Controlled Format String (CWE-134) vulnerability in Cisco Ios Xr. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 4% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

A vulnerability in the Cisco Discovery Protocol implementation within Cisco IOS XR Software stems from improper validation of string input in certain CDP message fields. This flaw, tracked under CWE-134 and CWE-787, can trigger a stack overflow when processing crafted packets. The affected component is the Layer 2 CDP handler on IOS XR devices, which runs with elevated privileges.

An unauthenticated attacker positioned on the same broadcast domain can exploit the issue by transmitting a single malicious CDP packet to an adjacent device. Successful exploitation yields arbitrary code execution with administrative rights or triggers a device reload, corresponding to the CVSS 8.8 vector AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

The Cisco Security Advisory cisco-sa-20200205-iosxr-cdp-rce details the flaw and available fixes, while the CISA Known Exploited Vulnerabilities catalog lists CVE-2020-3118 as actively used in the wild. Public exploit code has also appeared on Packet Storm.

EU & UK References

Vulnerability Data

A vulnerability in the Cisco Discovery Protocol implementation for Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to execute arbitrary code or cause a reload on an affected device. The vulnerability is due to improper validation of string…

more

input from certain fields in Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. A successful exploit could allow the attacker to cause a stack overflow, which could allow the attacker to execute arbitrary code with administrative privileges on an affected device. Cisco Discovery Protocol is a Layer 2 protocol. To exploit this vulnerability, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent).

CWE(s)
CWE-134CWE-787
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1211 Exploitation for Stealth Stealth
Adversaries may exploit vulnerabilities to evade detection by hiding activity, suppressing logging, or operating within trusted or unmonitored components.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

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Affected Assets

cisco
ios xr
5.2.5, 6.4.2, 6.5.3, 6.6.25, 7.0.1 · 6.6.0 — 6.6.12 · 7.0.0 — 7.0.2

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-16 Memory Protection
addresses: CWE-787

Out-of-bounds writes that corrupt control flow or inject shellcode are rendered non-executable by the same memory protections.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prevent external format strings via code review, static analysis, and safe APIs.

ID.RA-01 partial match
prevents

Vulnerability identification can discover existing format-string flaws but does not prevent their introduction.

PR.PS-02 partial match
prevents

Patching or replacing vulnerable software directly eliminates known instances of this coding weakness.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect format-string vulnerabilities before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates input validation and safe API usage that can prevent externally-controlled format strings.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify safe formatting functions and ban uncontrolled format strings.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles discourage dangerous string-handling patterns that lead to format-string issues.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly forbid the use of untrusted format strings and prescribe safe alternatives.

A.8.32 Change management partial match
prevents

Change management can enforce review gates that catch unsafe memory operations before deployment.

References