RHSA-2026:40574
Vulnerability from csaf_redhat - Published: 2026-07-16 01:07 - Updated: 2026-09-29 10:24A flaw was found in c-ares, an asynchronous resolver library. The 'ares_dns_name_parse()' function does not properly limit the total pointer hops or assembled name length when enforcing backward DNS compression pointers. A remote attacker, operating a malicious DNS server, can send a specially crafted DNS response containing a long descending pointer chain. This can lead to excessive CPU consumption, causing the single-threaded c-ares event loop to stall and resulting in a denial of service for DNS resolution.
| Product | Identifier | Version | Remediation |
|---|---|---|---|
| Unresolved product id: Red Hat Hardened Images:c-ares-0:1.34.8-2.hum1@aarch64 | — |
Vendor Fix
fix
|
|
| Unresolved product id: Red Hat Hardened Images:c-ares-0:1.34.8-2.hum1@src | — |
Vendor Fix
fix
|
|
| Unresolved product id: Red Hat Hardened Images:c-ares-0:1.34.8-2.hum1@x86_64 | — |
Vendor Fix
fix
|
|
| Unresolved product id: Red Hat Hardened Images:c-ares-devel-0:1.34.8-2.hum1@aarch64 | — |
Vendor Fix
fix
|
|
| Unresolved product id: Red Hat Hardened Images:c-ares-devel-0:1.34.8-2.hum1@x86_64 | — |
Vendor Fix
fix
|
A flaw was found in c-ares, an asynchronous resolver library. A remote attacker can send a specially crafted DNS response that causes the `ares_dns_parse()` function to trust attacker-controlled record counts without validating if the response contains enough bytes for the claimed records. This can lead to disproportionate heap memory reservation, resulting in a memory-amplification denial of service (DoS) by degrading or denying name resolution.
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"title": "c-ares: c-ares: CPU exhaustion denial of service via unbounded DNS name compression pointer chains"
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}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.