Unbound
CVE-2020-28935
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V5 - File Handling Symlink resolution safety
|
| Impact | CVSS score of 5.5 (MEDIUM). Attack characteristics: local attack vector, low complexity, low privileges required, no user interaction not required. |
| Exploit ScenarioDerived | Successful exploitation could compromise the medium-severity affected system. |
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Alert meAnalysisAI
NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. Rated medium severity (CVSS 5.5), this vulnerability is low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.
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Technical ContextAI · show details
This vulnerability is classified under CWE-59. NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system. Affected products include: Nlnetlabs Name Server Daemon, Nlnetlabs Unbound, Debian Debian Linux. Version information: version 1.12.0.
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Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
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What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)NVD
Unbound 1.6.4 through 1.9.4 contain a vulnerability in the ipsec module that can cause shell code execution after receiv
A crafted DNSKEY whose owner name is a compression pointer into its own RDATA overflows the digest buffer in the DNSSEC
Use-after-free in the DNSSEC validator of NLnet Labs Unbound resolver versions 1.19.1 through 1.25.0 allows remote attac
Remote denial of service in NLnet Labs Unbound recursive DNS resolver (versions up to and including 1.25.0) allows an at
Heap overflow denial-of-service in NLnet Labs Unbound recursive DNS resolver versions 1.14.0 through 1.25.0 allows remot
Heap-based memory corruption in NLnet Labs Unbound up to and including 1.26.0 lets a remote, unauthenticated attacker wh
Unbound before 1.9.4 accesses uninitialized memory, which allows remote attackers to trigger a crash via a crafted NOTIF
Remote denial of service in NLnet Labs Unbound 1.22.0 through 1.25.1 lets an unauthenticated client exhaust configured m
Remote denial-of-service in NLnet Labs Unbound 1.23.0 through 1.25.1 lets an attacker who controls a delegated DNS zone
Remote denial-of-service in NLnet Labs Unbound 1.9.0 through 1.25.1 allows an unauthenticated attacker to crash the recu
Heap buffer overflow in NLnet Labs Unbound 1.26.0 and earlier can be triggered when a resolver processing a large TCP-fr
Denial-of-service through algorithmic complexity attacks in NLnet Labs Unbound up to and including 1.26.0 can degrade or
GitHub PoC
Exploit-DB