Security readout for executives and security teams
Plain-English summary
CVE-2021-32816 is an availability issue in the ProtonMail Web Client. A crafted input could make the browser-side client spend excessive time processing a regular expression. The issue affects versions before 3.16.60 and is not described as exposing email contents or allowing account takeover.
Executive priority
Treat this as a moderate availability risk. Prioritize remediation if your organization runs, forks, or redistributes the ProtonMail Web Client. It does not warrant emergency response based on the provided evidence, but outdated client deployments should be upgraded.
Technical view
The vulnerability is a regular expression denial of service in the official AngularJS ProtonMail Web Client before 3.16.60. CVSS 3.1 is 6.5: network reachable, low complexity, no privileges, user interaction required, unchanged scope, and high availability impact only. It is classified as CWE-400 resource consumption.
Likely exposure
Exposure is limited to ProtonMail Web Client deployments, forks, or cached builds older than 3.16.60. The bundle does not establish exposure for ProtonMail-hosted production service at present.
Exploitation context
The CVE data does not show CISA KEV listing or cited evidence of active exploitation. User interaction is required, and the impact is denial of service rather than confidentiality or integrity compromise.
Researcher notes
The strongest evidence is the CVE record, GHSL advisory reference, and fix commit. Public data in the bundle identifies affected versions and impact, but does not provide active exploitation evidence. Avoid assuming broader ProtonMail service exposure without deployment-specific facts.
Mitigation direction
- Upgrade ProtonMail Web Client to version 3.16.60 or later.
- Confirm the deployed code includes fix commit 6687fbb867ef872c96cf4fde68cb6e9c58d3fddc.
- Replace or retire forks pinned to vulnerable pre-3.16.60 code.
- Clear stale client assets from deployment caches or CDNs.
- Monitor ProtonMail and GHSL advisories for additional vendor guidance.
Validation and detection
- Inventory all ProtonMail Web Client builds and record their exact versions.
- Check source or build metadata for the referenced fixed commit.
- Verify users are no longer served pre-3.16.60 client assets.
- Review forks for retained vulnerable regular expression logic.
- Use non-destructive regression testing outside production for availability-sensitive parsing paths.
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-400: 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-2021-32816 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://securitylab.github.com/advisories/GHSL-2021-027-redos-ProtonMail/CVE reference · x_refsource_CONFIRM
- https://github.com/ProtonMail/WebClient/commit/6687fbb867ef872c96cf4fde68cb6e9c58d3fddcCVE reference · x_refsource_MISC
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.
Uncontrolled Resource Consumption
Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.