Security readout for executives and security teams
Plain-English summary
A specially crafted URL inside an email body can make affected OTRS systems consume excessive CPU. That can degrade ticketing service quality or, in severe cases, halt the system. The issue is availability-focused; the supplied sources do not indicate data theft or active exploitation.
Executive priority
Treat as a moderate business-continuity risk for organizations dependent on OTRS for support operations. Prioritize patch validation for exposed mail-processing instances, especially where outages would affect customer service or incident response workflows.
Technical view
CVE-2021-21439 affects OTRS email-body URL handling and is classified as CWE-754. CVSS 3.1 is 6.5, with network attack vector, low complexity, no privileges required, user interaction required, and high availability impact. Affected ranges include ((OTRS)) Community Edition 6.0.1 and later 6.0.x, OTRS 7.0.26 and earlier, and OTRS 8.0.13 and earlier.
Likely exposure
Organizations are exposed if they run affected OTRS versions and process inbound emails into tickets. Internet-facing mail intake increases likelihood, but exploitation still depends on crafted email content being processed by the vulnerable system.
Exploitation context
The bundle reports a denial-of-service condition from specially designed URLs in email bodies. CVE metadata lists no privileges required and user interaction required. KEV is false, and the supplied sources do not support claiming active exploitation.
Researcher notes
Evidence supports an availability-only denial-of-service issue caused by URL handling in email bodies. The prompt does not include exploit details or exact fixed upstream versions, so validation should focus on version exposure and vendor or distribution advisory alignment.
Mitigation direction
- Inventory OTRS deployments and compare versions with the affected ranges.
- Review OTRS Security Advisory 2021-09 for vendor-supported updates or mitigations.
- For Debian-managed otrs2, review DLA 3551-1 and apply supported security updates.
- Monitor ticketing service CPU saturation and availability until remediation is complete.
- If no supported fix is available, seek vendor guidance before accepting untrusted inbound mail.
Validation and detection
- Confirm whether vulnerable OTRS versions are installed in production or support environments.
- Check whether inbound email-to-ticket processing is enabled on affected systems.
- Review logs and monitoring for CPU spikes during email processing.
- Verify remediation by confirming installed versions match vendor or distribution guidance.
- Document compensating controls if immediate update is not possible.
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-754: 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-2021-21439 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
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
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.
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:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://otrs.com/release-notes/otrs-security-advisory-2021-09/CVE reference
- [debian-lts-announce] 20230831 [SECURITY] [DLA 3551-1] otrs2 security updateCVE reference · mailing-list
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.
Improper Check for Unusual or Exceptional Conditions
Improper Check for Unusual or Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.