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CVE-2017-6739

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Cisco IOS and IOS XE Software. For every flaw being used in attacks, see Exploited flaws; for Cisco’s, see Cisco flaws being used in attacks.

CVE-2017-6739 is a security flaw in Cisco IOS and IOS XE Software, the operating system on Cisco’s routers and switches. Attackers can run their own code on Cisco IOS and IOS XE Software. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Mar 2022.[1]

Cisco IOS and IOS XE Software is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Cisco has published a fix or advice.

Description

CISA calls it an SNMP remote code execution in Cisco IOS and IOS XE Software. In its words: “The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE contains a vulnerability that could allow an authenticated, remote attacker to remotely execute code on an affected system or cause an affected system to reload.”[1]

The CVE record adds: “A vulnerability in the SNMP implementation of could allow an authenticated, remote attacker to cause a reload of the affected system or to remotely execute code. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the affected device.  The vulnerability is due to a buffer overflow in the affected code area. The vulnerability affects all versions of SNMP (versions 1, 2c, and 3). The attacker must know the SNMP read only community string (SNMP version 2c or earlier) or the user credentials (SNMPv3). An exploit could allow the attacker to execute arbitrary code and obtain full control of the system or to cause a reload of the affected system. Only traffic directed to the affected system can be used to exploit this vulnerability.”[2]

The underlying weakness is memory buffer error (CWE-119), in MITRE’s list of common software weaknesses.

It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Cisco’s advisory has them[3]. CISA names the product as Cisco IOS and IOS XE Software.

Most families won’t have Cisco IOS and IOS XE Software; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 3 Mar 2022, 1,690 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 24 Mar 2022 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 11%. That’s in the top 5% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Cisco has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]

  1. Check whether you use it.Cisco IOS and IOS XE Software is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 24 Mar 2022 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 11%.[4]

See also

Other Cisco IOS and IOS XE Software flaws

Other Cisco flaws

  • CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
  • CVE-2026-76519, Cisco Secure Email Gateway: relative path traversal ·
  • CVE-2026-76504, Cisco Catalyst SD-WAN Manager: hex encoding ·
  • CVE-2026-76460, Cisco Identity Services Engine: incorrect use of privileged APIs ·
  • CVE-2026-76461, Cisco Secure Email Gateway: SQL injection ·

Other memory buffer error flaws

  • CVE-2026-88779, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
  • CVE-2026-88772, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
  • CVE-2026-88771, Citrix NetScaler: improper input validation ·
  • CVE-2026-8452, Citrix NetScaler ADC and NetScaler Gateway: improper restriction of operations within the bounds of a memory buffer ·
  • CVE-2009-3459, Adobe Acrobat and Reader: heap-based buffer overflow ·

Added the same day

  • CVE-2022-20708, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
  • CVE-2022-20703, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
  • CVE-2022-20701, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
  • CVE-2022-20700, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
  • CVE-2022-20699, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·

Every Cisco flaw on CISA’s list · Everything added in March 2022

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Cisco IOS and IOS XE Software SNMP Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Mar 2022.
  2. ^ National Institute of Standards and Technology. “CVE-2017-6739 Detail”. National Vulnerability Database, published 17 Jul 2017.
  3. ^ Cisco. Advisories and fixes: sec.cloudapps.cisco.com, tools.cisco.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.109, percentile 95.9, 31 Oct 2026.
  5. CVE Program. “CVE-2017-6739”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.