CVE-2023-31137 [High] | Integer Overflow in Maradns

MaraDNS is open-source software that implements the Domain Name System (DNS). In version 3.5.0024 and prior, a remotely exploitable integer underflow vulnerability in the DNS packet decompression function allows an attacker to cause a Denial of Service by triggering an abnormal program termination. The vulnerability exists in the `decomp_get_rddata` function within the `Decompress.c` file. When handling a DNS packet with an Answer RR of qtype 16 (TXT record) and any qclass, if the `rdlength` is smaller than `rdata`, the result of the line `Decompress.c:886` is a negative number `len = rdlength - total;`. This value is then passed to the `decomp_append_bytes` function without proper validation, causing the program to attempt to allocate a massive chunk of memory that is impossible to allocate. Consequently, the program exits with an error code of 64, causing a Denial of Service. One proposed fix for this vulnerability is to patch `Decompress.c:887` by breaking `if(len <= 0)`, which has been incorporated in version 3.5.0036 via commit bab062bde40b2ae8a91eecd522e84d8b993bab58.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-27	1.05%	1.22%	+0.17%
2	2026-05-13	1.17%	1.05%	-0.12%
3	2026-02-01	—	1.17%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-27

1.05%

1.22%

+0.17%

2026-05-13

1.17%

1.05%

-0.12%

2026-02-01

—

1.17%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]
7.5	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	3.6	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

7.5

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

3.6

[email protected]

OS Trackers for CVE-2023-31137

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2023-31137 not yet assigned priority: Debian including 1 source packages (maradns), 1 status rows across 1 suites (bullseye): resolved 1.	https://security-tracker.debian.org/tracker/CVE-2023-31137
`ubuntu`	medium	CVE-2023-31137 medium priority: Ubuntu including 1 source packages (maradns), 8 status rows across 8 suites (bionic, focal, jammy, kinetic, lunar, trusty, upstream, xenial): released 5, ignored 2, needs-triage 1.	https://ubuntu.com/security/CVE-2023-31137

Affected software / configurations for CVE-2023-31137

Vendor	Product	Version	Raw CPE
maradns	maradns	< 3.4.10	cpe:2.3:a:maradns:maradns::::::::
maradns	maradns	>= 3.5.0001, < 3.5.0036	cpe:2.3:a:maradns:maradns::::::::
fedoraproject	fedora	37	cpe:2.3:o:fedoraproject:fedora:37:::::::*
fedoraproject	fedora	38	cpe:2.3:o:fedoraproject:fedora:38:::::::*
debian	debian_linux	10.0	cpe:2.3:o:debian:debian_linux:10.0:::::::*
debian	debian_linux	11.0	cpe:2.3:o:debian:debian_linux:11.0:::::::*

References for CVE-2023-31137

URL	Tags
https://github.com/samboy/MaraDNS/blob/08b21ea20d80cedcb74aa8f14979ec7c61846663/dns/Decompress.c#L886	Product
https://github.com/samboy/MaraDNS/commit/bab062bde40b2ae8a91eecd522e84d8b993bab58	Patch
https://github.com/samboy/MaraDNS/security/advisories/GHSA-58m7-826v-9c3c	Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/06/msg00019.html	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/[email protected]/message/3VSMLJX25MXGQ6A7UPOGK7VPUVDESPHL/	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/[email protected]/message/NB7LDZM5AGWC5BHHQHW6CP5OFNBBKFOQ/	Mailing List Third Party Advisory
https://www.debian.org/security/2023/dsa-5441	Mailing List Third Party Advisory

URL

CVE-2023-31137 | MaraDNS Integer Underflow Vulnerability in DNS Packet Decompression

Exploit prediction scoring system (EPSS) score for CVE-2023-31137

Common vulnerability scoring system (CVSS) metrics for CVE-2023-31137

Weakness enumeration for CVE-2023-31137

OS Trackers for CVE-2023-31137

Affected software / configurations for CVE-2023-31137

References for CVE-2023-31137