CVE-2021-34595 [High] | Memory Corruption in 750-823 Firmware

A crafted request with invalid offsets may cause an out-of-bounds read or write access in CODESYS V2 Runtime Toolkit 32 Bit full and PLCWinNT prior to versions V2.4.7.56, resulting in a denial-of-service condition or local memory overwrite.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.37%	0.85%	+0.48%
2	2025-10-25	0.49%	0.37%	-0.12%
3	2025-03-30	—	0.49%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.37%

0.85%

+0.48%

2025-10-25

0.49%

0.37%

-0.12%

2025-03-30

—

0.49%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
8.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	5.2	[email protected]
8.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	5.2	[email protected]
5.5	2.0	MEDIUM	`AV:N/AC:L/Au:S/C:N/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:S) A single authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	8.0	4.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

8.1

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

5.2

[email protected]

8.1

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

5.2

[email protected]

5.5

2.0

MEDIUM

AV:N/AC:L/Au:S/C:N/I:P/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:S): A single authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

8.0

4.9

[email protected]

Affected software / configurations for CVE-2021-34595

Vendor	Product	Version	Raw CPE
wago	750-823_firmware	< fw10	cpe:2.3:o:wago:750-823_firmware::::::::
wago	750-829_firmware	< fw17	cpe:2.3:o:wago:750-829_firmware::::::::
wago	750-831_firmware	< fw17	cpe:2.3:o:wago:750-831_firmware::::::::
wago	750-832_firmware	< fw10	cpe:2.3:o:wago:750-832_firmware::::::::
wago	750-852_firmware	< fw17	cpe:2.3:o:wago:750-852_firmware::::::::
wago	750-862_firmware	< fw10	cpe:2.3:o:wago:750-862_firmware::::::::
wago	750-880_firmware	< fw17	cpe:2.3:o:wago:750-880_firmware::::::::
wago	750-881_firmware	< fw17	cpe:2.3:o:wago:750-881_firmware::::::::
wago	750-882_firmware	< fw17	cpe:2.3:o:wago:750-882_firmware::::::::
wago	750-885_firmware	< fw17	cpe:2.3:o:wago:750-885_firmware::::::::
wago	750-889_firmware	< fw17	cpe:2.3:o:wago:750-889_firmware::::::::
wago	750-890_firmware	< fw10	cpe:2.3:o:wago:750-890_firmware::::::::
wago	750-891_firmware	< fw10	cpe:2.3:o:wago:750-891_firmware::::::::
wago	750-893_firmware	< fw10	cpe:2.3:o:wago:750-893_firmware::::::::
wago	750-8202_firmware	< fw20	cpe:2.3:o:wago:750-8202_firmware::::::::
wago	750-8203_firmware	< fw20	cpe:2.3:o:wago:750-8203_firmware::::::::
wago	750-8204_firmware	< fw20	cpe:2.3:o:wago:750-8204_firmware::::::::
wago	750-8206_firmware	< fw20	cpe:2.3:o:wago:750-8206_firmware::::::::
wago	750-8207_firmware	< fw20	cpe:2.3:o:wago:750-8207_firmware::::::::
wago	750-8208_firmware	< fw20	cpe:2.3:o:wago:750-8208_firmware::::::::
wago	750-8210_firmware	< fw20	cpe:2.3:o:wago:750-8210_firmware::::::::
wago	750-8211_firmware	< fw20	cpe:2.3:o:wago:750-8211_firmware::::::::
wago	750-8212_firmware	< fw20	cpe:2.3:o:wago:750-8212_firmware::::::::
wago	750-8213_firmware	< fw20	cpe:2.3:o:wago:750-8213_firmware::::::::
wago	750-8214_firmware	< fw20	cpe:2.3:o:wago:750-8214_firmware::::::::
wago	750-8216_firmware	< fw20	cpe:2.3:o:wago:750-8216_firmware::::::::
wago	750-8217_firmware	< fw20	cpe:2.3:o:wago:750-8217_firmware::::::::
codesys	codesys	< 1.1.9.22	cpe:2.3:a:codesys:codesys::::::::
codesys	plcwinnt	< 2.4.7.56	cpe:2.3:a:codesys:plcwinnt::::::::
codesys	runtime_toolkit	< 2.4.7.56	cpe:2.3:a:codesys:runtime_toolkit:::::::x86:*

References for CVE-2021-34595

URL	Tags
https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16878&token=e5644ec405590e66aefa62304cb8632df9fc9e9c&download=	Vendor Advisory

URL

CVE-2021-34595 | CODESYS V2 runtime: out-of-bounds read or write access may result in denial-of-service

Exploit prediction scoring system (EPSS) score for CVE-2021-34595

Common vulnerability scoring system (CVSS) metrics for CVE-2021-34595

Weakness enumeration for CVE-2021-34595

Affected software / configurations for CVE-2021-34595

References for CVE-2021-34595