CVE-2020-5135
CVE-2020-5135 is a security flaw in SonicWall SonicOS, SonicWall’s firewall and remote-access equipment. Attackers can run their own code on SonicWall SonicOS. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 15 Mar 2022, and says ransomware gangs have used it.[1]
SonicWall SonicOS 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. SonicWall has published a fix or advice.
Description
CISA calls it a buffer overflow in SonicWall SonicOS. In its words: “A buffer overflow vulnerability in SonicOS allows a remote attacker to cause Denial of Service (DoS) and potentially execute arbitrary code by sending a malicious request to the firewall.”[1]
The CVE record adds: “A buffer overflow vulnerability in SonicOS allows a remote attacker to cause Denial of Service (DoS) and potentially execute arbitrary code by sending a malicious request to the firewall. This vulnerability affected SonicOS Gen 6 version 6.5.4.7, 6.5.1.12, 6.0.5.3, SonicOSv 6.5.4.v and Gen 7 version 7.0.0.0.”[2]
The underlying weakness is buffer overflow (CWE-120), in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; SonicWall’s advisory has them[3]. CISA names the product as SonicWall SonicOS.
Most families won’t have SonicWall SonicOS; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 15 Mar 2022, 519 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 5 Apr 2022 to fix it.[1] CISA says ransomware gangs have used it.
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 27%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
SonicWall has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.SonicWall SonicOS 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.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 5 Apr 2022 to fix it.
- 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
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[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 27%.[4] |
See also
Other SonicWall SonicOS flaws
- CVE-2024-53704: SSLVPN improper authentication ·
- CVE-2024-40766: improper access control ·
Other SonicWall flaws
- CVE-2026-83549, SonicWall SMA1000 Appliances: OS command injection ·
- CVE-2026-83548, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2026-15410, SonicWall SMA1000 Appliances: code injection ·
- CVE-2026-15409, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2025-40602, SonicWall SMA1000 appliance: sMA1000 missing authorization ·
Other buffer overflow flaws
- CVE-2025-43520, Apple devices: classic buffer overflow ·
- CVE-2022-37055, D-Link Routers: buffer overflow ·
- CVE-2025-20333, Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense: secure firewall adaptive security appliance (ASA) and secure firewall threat defense (FTD) buffer overflow ·
- CVE-2020-15069, Sophos XG Firewall: buffer overflow ·
- CVE-2023-41064, Apple iOS, iPadOS, and macOS: imageIO buffer overflow ·
Added the same day
- CVE-2019-1405, Microsoft Windows: universal plug and play (UPnP) service privilege escalation ·
- CVE-2019-1322, Microsoft Windows: privilege escalation ·
- CVE-2019-1315, Microsoft Windows: error reporting manager privilege escalation ·
- CVE-2019-1253, Microsoft Windows: appX deployment server privilege escalation ·
- CVE-2019-1132, Microsoft Win32k: privilege escalation ·
Every SonicWall flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “SonicWall SonicOS Buffer Overflow Vulnerability”. Known Exploited Vulnerabilities Catalog, added 15 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2020-5135 Detail”. National Vulnerability Database, published 12 Oct 2020.
- ^ SonicWall. Advisories and fixes: psirt.global.sonicwall.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.269, percentile 98.0, 31 Oct 2026.
- CVE Program. “CVE-2020-5135”. 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.