FERRAMENTAS LINUX: BIND 9 Security Update: Mitigate CPU Exhaustion Vulnerability CVE-2025-8677

Mitigate CVE-2025-8677, a high-severity BIND 9 vulnerability causing CPU exhaustion via malformed DNSKEY records. Learn affected versions, patching steps, and exploit details.

A single, malformed DNSKEY record can now cripple an organization's DNS resolution. The recently patched vulnerability CVE-2025-8677 exposes a critical flaw in BIND 9, threatening Denial-of-Service (DoS) conditions through remote CPU exhaustion.

This high-severity issue, with a CVSS score of 7.5, affects a wide range of BIND 9 versions and requires immediate attention from system administrators globally .

The Internet Systems Consortium (ISC) has released a coordinated security advisory, urging users to patch recursive resolvers to prevent potential exploitation. This advisory provides a technical deep dive into the vulnerability, its impact, and step-by-step remediation guidance.

Vulnerability Overview & Technical Details

CVE-2025-8677 is a resource exhaustion vulnerability located within the DNSSEC validation logic of BIND 9. The flaw triggers when a recursive resolver queries a maliciously crafted authoritative DNS zone containing specific malformed DNSKEY records.

During the DNSSEC validation process, these records cause the resolver to perform computationally expensive operations, leading to severe CPU consumption and rendering the service unresponsive.

Aspect	Details
CVE ID	CVE-2025-8677
CVSS v3.1 Score	7.5 (High)
Attack Vector	Remote, Network
Impact	High Availability Impact (CPU Exhaustion)
Key Target	Recursive Resolvers performing DNSSEC validation

Affected Software and Versions

The following versions of BIND 9 are confirmed vulnerable and require patching :

9.18.x series: 9.18.0 through 9.18.39
9.20.x series: 9.20.0 through 9.20.13
9.21.x series: 9.21.0 through 9.21.12
Supported Preview Editions: 9.18.11-S1 through 9.18.39-S1 and 9.20.9-S1 through 9.20.13-S1

Note for Administrators: Authoritative-only BIND servers are not affected. The vulnerability specifically impacts recursive resolver configurations .

Patched Versions and Update Instructions

ISC has released fixed versions that resolve this vulnerability. Users should update immediately to one of the following patched releases :

BIND 9.18.40+
BIND 9.20.14+
BIND 9.21.13+

For users operating on Fedora 43, the update is available via the dnf package manager. The bind9-next package has been updated to version 9.21.14 which includes the fix for CVE-2025-8677 .

Update Command for Fedora:

sudo dnf upgrade --advisory FEDORA-2025-b68f7f541d

After applying the update, a restart of the BIND service (named) is required for the patch to take effect .

Attack Mechanics and Exploitation Scenario

Understanding the attack flow is crucial for risk assessment. Successful exploitation requires an attacker to control or compromise an authoritative DNS zone. By populating this zone with specially malformed DNSKEY records, they can create a booby-trapped domain.

When a vulnerable BIND 9 recursive resolver receives a query for this domain—either directly or through a cached reference—it fetches the zone's records and initiates DNSSEC validation.

The malformed structure of the DNSKEY records causes the validation algorithm to enter an inefficient state, consuming 100% of available CPU resources. This can lead to a complete failure of the DNS resolution service for all clients depending on that resolver .

Frequently Asked Questions (FAQ)

Q: Can this vulnerability be exploited to steal data or poison the cache?

A: No. CVE-2025-8677 is a pure Availability issue, leading only to CPU exhaustion and Denial-of-Service. It does not directly allow for data theft, cache poisoning, or unauthorized access .

Q: Is there a temporary workaround if I cannot patch immediately?

A: Public sources indicate there is no known workaround. The only effective mitigation is to update BIND 9 to a patched version .

Q: How is this different from other DNS vulnerabilities like KeyTrap?

A: While the overall impact—CPU exhaustion—is similar to past vulnerabilities like (), the root cause is distinct. CVE-2025-8677 is specifically triggered by the processing of malformed DNSKEY records during validation .

Q: Are public exploits available for this vulnerability?

A: Yes. According to security advisories, public proof-of-concept (PoC) exploits for CVE-2025-8677 have been published on , increasing the likelihood of widespread exploitation attempts .