Product Overview
libssh is an open-source library written in C that implements the SSH protocol and SFTP client/server capabilities. The library is commonly embedded into software that requires secure remote connectivity, automated file transfer, configuration management, or secure remote command execution.
Many infrastructure management tools, backup solutions, automation frameworks, network appliances, and embedded systems rely on libssh for SSH functionality.
A vulnerability was identified in the SFTP extension handling logic where improper validation of array indexes allows memory to be read outside the intended buffer boundaries. Under certain conditions this behaviour may expose unintended memory contents or cause application instability.
Vulnerability Details
| Field | Information |
|---|---|
| CVE ID | CVE-2026-3731 |
| Product | libssh |
| Component | SFTP Extension Handler |
| Vulnerability Type | Out-of-Bounds Read |
| Severity | High |
| CVSS Score | ~5.3 |
| Attack Vector | Network |
| Privileges Required | None |
| User Interaction | None |
| Exploitability | Moderate |
| Exploit Availability | No confirmed public exploit |
| Affected Versions | libssh ≤ 0.11.3 |
| Fixed Versions | 0.11.4, 0.12.0 |
Technical Description
The vulnerability exists in the logic responsible for processing SFTP extension information returned by an SSH server during the SFTP initialization phase.
When an SFTP connection is established, the server sends a version packet containing extension names and associated data. The libssh client stores these extensions internally within a list.
Two internal helper functions are used to retrieve these extension entries:
sftp_extensions_get_name()
sftp_extensions_get_data()
The functions accept an index parameter (idx) representing the extension entry that should be returned.
In vulnerable versions of libssh, this index value was not consistently validated against the total number of extensions stored in memory.
If an invalid index value is processed, memory outside the extension array may be accessed. This behaviour results in an out-of-bounds read condition.
Although memory is not overwritten, the application may read unintended portions of memory. Depending on how the returned data is handled by the application, the behaviour may lead to:
- information disclosure
- abnormal application behaviour
- process crashes
- potential denial of service
Attack Vector
The vulnerability can be triggered remotely when a system connects to a malicious or compromised SSH/SFTP server.
The attack sequence is generally performed during the SFTP session initialization phase.
- A client application initiates an SSH session.
- The SFTP subsystem is started.
- The server returns a manipulated SSH_FXP_VERSION packet containing crafted extension data.
- The extension metadata causes the client to store unexpected extension values.
- When the application attempts to query extension details, the invalid index results in memory being read outside the expected buffer.
Because the vulnerable code is executed automatically during the SFTP handshake, exploitation can occur without user interaction once the connection is initiated.
Potential Impact
The following impacts may occur if exploitation is successful:
- Exposure of unintended memory content
- Crashes in applications that rely on libssh
- Disruption of automated SSH workflows
- Potential information leakage useful for follow-up attacks
Systems using libssh for automated backup, infrastructure orchestration, or network device management may be affected if they connect to untrusted SSH endpoints.
Proof of Concept
A publicly distributed exploit has not been widely observed. However, the vulnerability can be reproduced in a controlled testing environment.
A proof-of-concept demonstration can be created by implementing a custom SSH server that returns crafted SFTP extension metadata.
Example conceptual behaviour of the malicious server:
SSH_FXP_VERSION
version: 3
extension_count: manipulated_value
extension_name: test_extension
extension_data: crafted_payload
When the client library attempts to retrieve extension entries beyond the allocated list, memory outside the expected region is read.
Such proof-of-concept testing should only be performed within controlled research environments for educational or defensive security purposes.
Detection
Indicators of Suspicious Behaviour
The following operational indicators may suggest attempts to exploit the vulnerability:
- abnormal SFTP negotiation packets
- unexpected extension metadata during SFTP initialization
- application crashes during SFTP session setup
- segmentation faults inside libssh SFTP functions
Log Sources
Monitoring should include the following log sources:
- SSH client application logs
- Linux system logs (syslog / journald)
- endpoint crash reports
- application debugging logs
- network intrusion detection systems
- packet capture telemetry
Detection Rules
Network Detection Rule (Suricata / Snort Style)
alert tcp any any -> any 22
(
msg:"Potential libssh SFTP extension manipulation attempt";
flow:to_client,established;
content:"SSH_FXP_VERSION";
pcre:"/extension.*\x00\x00\x00/s";
sid:9003731;
rev:1;
)
Splunk Detection Query
index=network_logs
dest_port=22
("SSH_FXP_VERSION" OR "SFTP extension")
| stats count by src_ip dest_ip
| where count > 50
Elastic / Kibana Detection Query
network.transport:tcp AND destination.port:22 AND
message:"SFTP extension"
Endpoint Crash Monitoring Query
index=linux_syslog
("segfault" OR "memory access violation")
AND ("libssh" OR "sftp")
Mitigation
If immediate upgrading is not possible, the following mitigation steps can reduce exposure:
- restrict SSH connections to trusted hosts
- disable automated connections to unknown SFTP servers
- monitor abnormal SFTP handshake traffic
- isolate systems performing automated file transfers
Patch / Upgrade
The vulnerability has been corrected by implementing strict bounds validation on extension index values before memory access occurs.
Systems using libssh should be upgraded to a patched release.
Official patch / upgrade source:
Crypt::Sodium::XS – Integer Overflow Leading to Buffer Overflow Risk
CVE-2026-30910
Product Overview
Crypt::Sodium::XS is a Perl module that provides high-performance bindings to the libsodium cryptographic library. The module enables Perl applications to perform secure encryption, authentication, hashing, and key management operations.
It is commonly integrated into applications responsible for:
- secure communication systems
- encrypted storage platforms
- authentication services
- API security frameworks
- cryptographic token generation
A vulnerability was identified in the handling of buffer size calculations used during encryption operations, where integer arithmetic may overflow when processing extremely large values.
Vulnerability Details
| Field | Information |
|---|---|
| CVE ID | CVE-2026-30910 |
| Product | Crypt::Sodium::XS |
| Vulnerability Type | Integer Overflow leading to Buffer Overflow |
| Severity | High |
| Attack Vector | Network / Input based |
| Privileges Required | None |
| User Interaction | None |
| Exploitability | High |
| Exploit Availability | No confirmed public exploit |
| Affected Versions | Versions prior to 0.000042 |
| Fixed Versions | 0.000042 and later |
Technical Description
The vulnerability occurs in encryption routines where memory buffers are allocated based on calculated sizes.
The size of the output buffer is derived from values such as:
- message length
- authentication tag length
- cryptographic overhead
In affected versions, the calculation was performed using standard integer arithmetic.
A simplified conceptual calculation resembles the following:
buffer_size = message_length + crypto_overhead
If the value of message_length becomes extremely large or intentionally manipulated, the arithmetic operation may exceed the maximum representable integer value.
When this occurs, the result wraps around and produces a much smaller value than expected.
As a consequence:
- An undersized memory buffer is allocated.
- Encryption routines proceed to write the full encrypted output.
- Memory beyond the allocated buffer is overwritten.
This behaviour results in a buffer overflow condition which may corrupt adjacent memory structures.
Attack Vector
Exploitation requires the ability to provide input values that influence encryption buffer calculations.
Possible scenarios include:
- encryption services exposed through APIs
- web services encrypting user-supplied content
- applications encrypting uploaded data
- message processing systems handling untrusted input
An attacker may intentionally submit extremely large input values that trigger integer overflow during buffer size calculations.
Potential Impact
If exploitation occurs, the following outcomes may be observed:
- application crashes
- memory corruption
- service disruption
- cryptographic operation failures
- possible remote code execution in specific conditions
Because the vulnerability occurs in memory handling routines, the exact impact may vary depending on how the affected application uses the module.
Proof of Concept
Public exploit code has not been widely released. However, the vulnerability can be demonstrated through controlled testing.
A proof-of-concept scenario can involve passing extremely large message lengths to encryption routines.
Example conceptual payload:
payload_size = 0xffffffff
key = valid_key
nonce = valid_nonce
During encryption, the internal buffer calculation may overflow and lead to memory corruption.
Such testing should only be performed within isolated research environments for defensive security education and vulnerability analysis.
Detection
Indicators of Suspicious Behaviour
Systems affected by this issue may display:
- segmentation faults in Perl processes
- memory corruption warnings
- abnormal termination of encryption services
- unusually large payload submissions
Log Sources
The following telemetry sources are useful for monitoring exploitation attempts:
- application logs
- Perl runtime logs
- Linux crash reports
- memory protection alerts
- API gateway logs
- web server logs
- endpoint detection telemetry
Detection Rules
Splunk Detection Query
index=application_logs
("Crypt::Sodium::XS" OR "libsodium")
("segmentation fault" OR "memory corruption" OR "buffer overflow")
Elastic Detection Query
process.name:perl AND
(message:"memory corruption" OR message:"segmentation fault")
Web Log Detection Query
index=web_logs
request_size > 100000000
| stats count by src_ip uri
Endpoint Crash Monitoring Query
index=system_logs
("segfault" OR "buffer overflow")
AND ("perl" OR "libsodium")
Mitigation
If upgrading cannot be performed immediately, the following defensive measures are recommended:
- enforce strict input validation on data sizes
- limit maximum payload size accepted by applications
- monitor abnormal memory errors
- isolate encryption services from untrusted input sources
Patch / Upgrade
The vulnerability was resolved by implementing safe integer arithmetic and improved buffer length validation during cryptographic operations.
Systems using the module should upgrade to a patched release.
Official upgrade source:
https://metacpan.org/release/Crypt-Sodium-XS
