Description
c-ares is an asynchronous resolver library. Prior to 1.34.7, ares_dns_parse() trusts the attacker-controlled ANCOUNT, NSCOUNT, and ARCOUNT fields before confirming that the DNS response contains enough bytes for the claimed records. Because process_answer() invokes parsing before transaction ID and question validation, a malicious DNS response can cause ares_dns_record_rr_prealloc() and ares_array_set_size() to reserve disproportionate heap memory for a tiny message. Repeated responses create large allocation and release cycles that can degrade or deny name 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 | No fix yet | — |
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 |
|---|---|---|---|
| Red Hat Hardened Images 1 | c-ares +1 | 1.34.8-2.hum1 | RHSA-2026:40574 |
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 |
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 |
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 9
- 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-2026:23364-1 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
References
- https://github.com/c-ares/c-ares/security/advisories/GHSA-jv8r-gqr9-68wj
- https://github.com/c-ares/c-ares/pull/1134
- https://github.com/c-ares/c-ares/commit/e47c203f91cd8b749c8736bc18d75a31ffdec8f4
- https://github.com/c-ares/c-ares/commit/eaded4cb200b2a5f8d73f11021ff7c8d6968aaab
- https://github.com/c-ares/c-ares/releases/tag/v1.34.7