Security readout for executives and security teams
Plain-English summary
A malicious SSH/SFTP server, or someone intercepting that connection, can make libssh2 read past a heap buffer. This may crash an affected client or expose limited process memory. The issue matters most where systems connect to untrusted or compromised SFTP endpoints.
Executive priority
Treat as a high-priority dependency update for systems that initiate SFTP connections. The business risk is service disruption and possible limited memory disclosure from clients that trust hostile or intercepted SSH servers.
Technical view
libssh2 through 1.11.1 has a CWE-125 heap over-read in sftp_symlink() handling SSH_FXP_NAME responses for SFTP READLINK and REALPATH. A crafted response can set link_len larger than available packet data, causing memcpy to read beyond the buffer. The bundle identifies commit 2dae302 as the fix.
Likely exposure
Exposure is likely in software that embeds or links libssh2 and acts as an SFTP client, especially automation, backup, transfer, or integration tools that connect to third-party SSH servers.
Exploitation context
The CVE is not marked KEV, and the supplied sources do not show active exploitation. Exploitation requires a malicious SSH server or man-in-the-middle position, but no credentials or user interaction are listed in the CVSS vector.
Researcher notes
Evidence supports a packet-length validation flaw in sftp_symlink() with impact limited to over-read disclosure or crash. The provided bundle names a fixing commit but not a fixed release version. Avoid claiming exploitation in the wild unless new KEV or vendor evidence appears.
Mitigation direction
- Upgrade libssh2 to a vendor release containing commit 2dae302 when available.
- Apply the referenced patch commit if maintaining a custom build.
- Review distribution advisories for backported libssh2 fixes.
- Restrict SFTP connections to trusted servers where feasible.
- Enforce SSH host key verification to reduce man-in-the-middle risk.
Validation and detection
- Inventory direct and transitive libssh2 usage across applications and appliances.
- Check whether deployed libssh2 is through 1.11.1 or before commit 2dae302.
- Identify workflows using SFTP READLINK or REALPATH against external servers.
- Confirm vendor, OS, or container packages include the fix or backport.
- Prioritize internet-facing automation that connects to third-party SFTP endpoints.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-125: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-15661 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.3 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
2 official scoresWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N——VulnCheckCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H2.24.2VulnCheckVulnerability scoring details
Base CVSS 4.0 score
8.3HighVector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Researcher Pull RequestCVE reference, VulnCheck · issue-tracking
- Maintainer Pull RequestCVE reference, VulnCheck · issue-tracking
- Patch CommitCVE reference, VulnCheck · patch
- https://www.vulncheck.com/advisories/libssh2-heap-buffer-over-read-via-sftp-symlink-in-sftp-cCVE reference, VulnCheck · third-party-advisory
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.