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CVE-2026-69186— c-ares: Memory-amplification denial of service via unvalidated DNS header record counts

Quick assessment

Affected
c-ares c-ares
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

c-ares 是一个异步 DNS 解析库。在 1.34.7 之前， 函数在确认 DNS 响应中包含足够字节以容纳其所声称的记录数量之前，就信任了攻击者可控的 、 和 字段。由于 在验证事务 ID 和问题字段之前就会调用解析逻辑，因此一个恶意的 DNS 响应可能导致 和 为一条很小的消息预留出与其实际大小不成比例的大量堆内存。反复接收此类响应会引发频繁的内存分配与释放周期，从而可能降低域名解析性能，甚至导致 DNS 解析服务不可用（拒绝服务），但不会引起内存损坏或信息泄露。该问题已在 1.34.7 版本中修复。

CVSS 5.3 · Medium EPSS 0.47% · P40

Affected Version Matrix 1

VendorProduct Version RangeStatus
c-ares c-ares < 1.34.7 affected
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I. Basic Information for CVE-2026-69186

Vulnerability Information
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Vulnerability Title
c-ares: Memory-amplification denial of service via unvalidated DNS header record counts
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
c-ares c-ares < 1.34.7 -

II. Public POCs for CVE-2026-69186

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III. Intelligence Information for CVE-2026-69186

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Patches & Fixes for CVE-2026-69186 (3)

Vendor Pages for CVE-2026-69186 (1)

Other References for CVE-2026-69186 (1)

IV. Related Vulnerabilities

Same product: c-ares
Same vendor: c-ares
Same weakness: CWE-400