Security readout for executives and security teams
Plain-English summary
A user with permitted TFTP access may manipulate relative file paths to reach files outside the intended TFTP directory. Potential confidentiality and integrity impact is limited, with no availability impact identified. Systems not using the affected TFTP file modules are unlikely to be exposed.
Executive priority
Treat as routine but time-bound remediation. Prioritize externally reachable or broadly accessible TFTP deployments and systems protecting sensitive files. Lower priority is reasonable where TFTP is disabled, isolated, or inaccessible to untrusted users.
Technical view
CVE-2026-21620 is a CWE-23 relative path traversal in Erlang/OTP tftp_file modules. The flaw weakens directory isolation during TFTP file operations. CVSS 4.0 rates it 2.3: network-reachable, low complexity, requiring privileges and specific conditions, with low confidentiality and integrity impact.
Likely exposure
Exposure requires affected Erlang/OTP, tftp, or inets versions, use of the tftp_file modules, network reachability, and an attacker with permitted access. OTP releases from 17.0 through vulnerable branch versions are affected; precise exposure should be confirmed against the vendor advisory.
Exploitation context
The supplied sources do not report active exploitation, and the CVE is not listed as KEV. Exploitation requires low privileges and an additional precondition. The primary risk is unauthorized access to or modification of files outside the configured TFTP directory.
Researcher notes
The vulnerable files are lib/tftp/src/tftp_file.erl and src/tftp_file.erl. Public patch commits and pull request 10706 are available for code-level review. The supplied evidence establishes path traversal but does not describe observed attacks or quantify reachable files under particular deployments.
Mitigation direction
- Upgrade OTP 28 to 28.3.2 or later.
- Upgrade OTP 27 to 27.3.4.8 or later.
- Upgrade OTP 26 to 26.2.5.17 or later.
- Update standalone tftp or inets components according to the vendor advisory.
- Restrict TFTP access to trusted networks and authorized users until updated.
Validation and detection
- Inventory Erlang/OTP, tftp, and inets versions across deployed systems.
- Confirm whether tftp_file modules are enabled and used.
- Identify which networks and identities can reach the TFTP service.
- Compare installed versions with each affected branch's fixed release.
- Review TFTP and file-access logs for unexpected paths or out-of-directory access.
- After updating, verify the runtime reports the intended fixed version.
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-23: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. 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 lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-21620 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
- Low
- CVSS
- 2.3 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/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
1 official scoreWe 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:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N——EEFVulnerability scoring details
Base CVSS 4.0 score
2.3LowVector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
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
- https://github.com/erlang/otp/security/advisories/GHSA-hmrc-prh3-rpvpCVE reference, EEF · vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-21620.htmlCVE reference, EEF · related
- https://osv.dev/vulnerability/EEF-CVE-2026-21620CVE reference, EEF · related
- https://www.erlang.org/doc/system/versions.html#order-of-versionsCVE reference, EEF · x_version-scheme
- https://github.com/erlang/otp/pull/10706CVE reference, EEF · patch
- https://github.com/erlang/otp/commit/696fdec922661d4a3cc528fc34bc24fae8d4ad8aCVE reference, EEF · patch
- https://github.com/erlang/otp/commit/3970738f687325138eb75f798054fa8960ac354eCVE reference, EEF · patch
- https://github.com/erlang/otp/commit/655fb95725ba2fb811740b57e106873833824344CVE reference, EEF · patch
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.