Description
c-ares is an asynchronous resolver library. Prior to 1.34.7, ares_dns_name_parse() enforces backward DNS compression pointers but does not bound the total pointer hops or assembled name length. A malicious DNS server can send a response containing a long descending pointer chain and many resource records whose NAME or RDATA fields refer to the chain, causing repeated decompression work that grows quadratically with message size. A single crafted response can stall the single-threaded c-ares event loop and deny DNS resolution, without causing memory corruption or information disclosure. This issue is fixed in version 1.34.7.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| c-ares | c-ares | < 1.34.7 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | c-ares | 1.34.7-1 | — |
| Debian 13 | c-ares | 1.34.9-1~deb13u1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | c-ares | 1.34.6-1ubuntu0.2 | USN-8951-1 |
| Ubuntu 24.04 LTS | c-ares | 1.27.0-1.0ubuntu1.1 | USN-8951-1 |
| Ubuntu 22.04 LTS | c-ares | 1.18.1-1ubuntu0.22.04.4 | USN-8951-1 |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | c-ares | 1.15.0-1ubuntu0.5+esm1 | USN-8951-1 |
| Ubuntu Pro 18.04 LTS | c-ares | 1.14.0-1ubuntu0.2+esm3 | USN-8951-1 |
| Ubuntu Pro 16.04 LTS | c-ares | 1.10.0-3ubuntu0.2+esm4 | USN-8951-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10 | c-ares +1 | 1.34.6-5.el10_3.2 | RHSA-2026:98629 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 10.2 EUS | c-ares +1 | 1.34.6-2.el10_2.2 | RHSA-2026:99168 |
| Red Hat Hardened Images 1 | c-ares +1 | 1.34.8-2.hum1 | RHSA-2026:40574 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 10 | c-ares +1 | 1.34.6-5.el10_3.2 | RLSA-2026:98629 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES 15 SP6 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES 15 SP5 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES 15 SP4 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES 12 SP5 | libcares2 | 1.9.1-9.24.1 | SUSE-SU-2026:3872-1 |
Show 12 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | c-ares | 1.34.8-160000.1.1 | SUSE-SU-2026:23597-1 |
| SLES for SAP 15 SP6 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES for SAP 15 SP5 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES for SAP 15 SP4 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLES 16.0 | c-ares | 1.34.8-160000.1.1 | SUSE-SU-2026:23597-1 |
| SLE Micro 6.1 | c-ares | 1.34.8-slfo.1.1_1.1 | SUSE-SU-2026:23414-1 |
| SLE Micro 6.0 | c-ares | 1.34.8-1.1 | SUSE-SU-2026:23364-1 |
| SLE Micro 5.5 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLE Micro 5.4 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLE Micro 5.3 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLE HPC 15 SP5 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
| SLE HPC 15 SP4 | c-ares | 1.34.8-150000.3.29.1 | SUSE-SU-2026:4021-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | c-ares | 1.34.8-1.1 | openSUSE-SU-2026:11593-1 |
| openSUSE Leap 16.0 | c-ares | 1.34.8-160000.1.1 | openSUSE-SU-2026:21721-1 |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | nodejs22 +4 | 1:22.23.2-1.amzn2023.0.2 | ALAS2023-2026-2060 |
| Amazon Linux 2023 | nodejs22-npm | 1:10.9.8-1.22.23.2.1.amzn2023.0.2 | ALAS2023-2026-2060 |
| Amazon Linux 2023 | nodejs24 +4 | 1:24.18.1-1.amzn2023.0.2 | ALAS2023-2026-2059 |
| Amazon Linux 2023 | nodejs24-npm | 1:11.16.0-1.24.18.1.1.amzn2023.0.2 | ALAS2023-2026-2059 |
| Amazon Linux 2023 | v8-12.4-devel | 3:12.4.254.21-1.22.23.2.1.amzn2023.0.2 | ALAS2023-2026-2060 |
| Amazon Linux 2023 | v8-13.6-devel | 3:13.6.233.17-1.24.18.1.1.amzn2023.0.2 | ALAS2023-2026-2059 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | c-ares | 1.34.8-1 | — |
| Azure Linux 3 | fluent-bit | No fix yet | — |
Advisories 15
- RHSA-2026:99168 Red Hat Security Advisory: c-ares security update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RHSA-2026:98629 Red Hat Security Advisory: c-ares security update Red Hat Security Advisories (RHSA) · Nov 13, 2026
- RLSA-2026:98629 Important: c-ares security update Rocky Linux Security Advisories · Nov 13, 2026
- WID-SEC-2026-4542 Red Hat Enterprise Linux: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- USN-8951-1 c-ares vulnerabilities Ubuntu Security Notices (USN) · Oct 22, 2026
- RHSA-2026:40574 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 17, 2026
- SUSE-SU-2026:23597-1 Security update for c-ares SUSE / openSUSE Security Updates · Sep 29, 2026
- SUSE-SU-2026:23414-1 Security update for c-ares SUSE / openSUSE Security Updates · Sep 14, 2026
- SUSE-SU-2026:4021-1 Security update for c-ares SUSE / openSUSE Security Updates · Sep 13, 2026
- SUSE-SU-2026:3872-1 Security update for libcares2 SUSE / openSUSE Security Updates · Sep 10, 2026
- SUSE-SU-2026:23364-1 Security update for c-ares SUSE / openSUSE Security Updates · Sep 10, 2026
- openSUSE-SU-2026:21721-1 Security update for c-ares SUSE / openSUSE Security Updates · Sep 2, 2026
- openSUSE-SU-2026:11593-1 c-ares-devel-1.34.8-1.1 on GA media SUSE / openSUSE Security Updates · Aug 26, 2026
- ALAS2023-2026-2059 Important: nodejs24 security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 21, 2026
- ALAS2023-2026-2060 Important: nodejs22 security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 17, 2026
References
- https://github.com/c-ares/c-ares/security/advisories/GHSA-pjmc-gx33-gc76
- https://github.com/c-ares/c-ares/pull/1164
- https://github.com/c-ares/c-ares/pull/1210
- https://github.com/c-ares/c-ares/commit/5c8341ba6ff3a8e4e4dfd616f8ed0418838b8b7b
- https://github.com/c-ares/c-ares/commit/f1288bbc70e9a1e0a77134c2382157e52d326aea
- https://github.com/c-ares/c-ares/releases/tag/v1.34.7