CVE-2020-5235 [Medium] | Out-of-bounds Read in Nanopb

There is a potentially exploitable out of memory condition In Nanopb before 0.4.1, 0.3.9.5, and 0.2.9.4. When nanopb is compiled with PB_ENABLE_MALLOC, the message to be decoded contains a repeated string, bytes or message field and realloc() runs out of memory when expanding the array nanopb can end up calling `free()` on a pointer value that comes from uninitialized memory. Depending on platform this can result in a crash or further memory corruption, which may be exploitable in some cases. This problem is fixed in nanopb-0.4.1, nanopb-0.3.9.5, nanopb-0.2.9.4.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.56%	1.68%	+1.13%
2	2025-11-21	0.81%	0.56%	-0.26%
3	2025-11-18	—	0.81%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.56%

1.68%

+1.13%

2025-11-21

0.81%

0.56%

-0.26%

2025-11-18

—

0.81%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.5	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:L` 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:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:C) Breaking this can reach past the original component and bite other resources—bigger blast radius. Confidentiality (C:L) Some sensitive info could get out, but not a total data dump. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:L) Might cause slowdowns, glitches, or partial disruption—not a full brick.	2.2	3.7	[email protected]
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:N) No account or special rights needed—anonymous or random user is enough. 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:H) Serious risk that confidential data gets exposed in a big 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.	3.9	5.9	[email protected]
7.5	2.0	HIGH	`AV:N/AC:L/Au:N/C:P/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:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	10.0	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.5

3.1

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:L 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:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C): Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L): Some sensitive info could get out, but not a total data dump.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:L): Might cause slowdowns, glitches, or partial disruption—not a full brick.

2.2

3.7

[email protected]

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:N): No account or special rights needed—anonymous or random user is enough.
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:H): Serious risk that confidential data gets exposed in a big 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.

3.9

5.9

[email protected]

7.5

2.0

HIGH

AV:N/AC:L/Au:N/C:P/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:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

6.4

[email protected]

OS Trackers for CVE-2020-5235

vendor	priority	summary	link
`debian`	unimportant	CVE-2020-5235 unimportant priority: Debian including 1 source packages (nanopb), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2020-5235
`suse`	medium	CVE-2020-5235 severity moderate: SUSE including 3 source package names (libprotobuf-nanopb0-0.4.5-1.3, nanopb-devel-0.4.5-1.3, nanopb-source-0.4.5-1.3), 3 product×package rows across 1 product lines (openSUSE Tumbleweed): Fixed 3.	https://www.suse.com/security/cve/CVE-2020-5235/

Affected software / configurations for CVE-2020-5235

Vendor	Product	Version	Raw CPE
nanopb_project	nanopb	< 0.2.9.4	cpe:2.3:a:nanopb_project:nanopb::::::::
nanopb_project	nanopb	>= 0.3.0, < 0.3.9.5	cpe:2.3:a:nanopb_project:nanopb::::::::
nanopb_project	nanopb	>= 0.4.0, < 0.4.1	cpe:2.3:a:nanopb_project:nanopb::::::::

References for CVE-2020-5235

URL	Tags
https://github.com/nanopb/nanopb/commit/45582f1f97f49e2abfdba1463d1e1027682d9856	Patch Third Party Advisory
https://github.com/nanopb/nanopb/commit/7b396821ddd06df8e39143f16e1dc0a4645b89a3	Patch Third Party Advisory
https://github.com/nanopb/nanopb/commit/aa9d0d1ca78d6adec3adfeecf3a706c7f9df81f2	Patch Third Party Advisory
https://github.com/nanopb/nanopb/security/advisories/GHSA-gcx3-7m76-287p	Patch Third Party Advisory

URL

CVE-2020-5235 | Out-of-memory condition in Nanopb is potentially exploitable

Exploit prediction scoring system (EPSS) score for CVE-2020-5235

Common vulnerability scoring system (CVSS) metrics for CVE-2020-5235

Weakness enumeration for CVE-2020-5235

OS Trackers for CVE-2020-5235

Affected software / configurations for CVE-2020-5235

References for CVE-2020-5235