Vulnerability in Useplunk Plunk
CVE-2026-34975
Plunk is an open-source email platform built on top of AWS SES. Prior to 0.8.0, a CRLF header injection vulnerability was discovered in SESService.ts, where user-supplied values for from.name, subject, custom header keys/values, and attachment filenames were interpolated directly into raw MIME messages without sanitization. An authenticated API user could inject arbitrary email headers (e.g. Bcc, Reply-To) by embedding carriage return/line feed characters in these fields, enabling silent email forwarding, reply redirection, or sender spoofing. The fix adds input validation at the schema level to reject any of these fields containing \r or \n characters, consistent with the existing validation already applied to the contentId field. This vulnerability is fixed in 0.8.0.
Vulnerability class: CRLF Injection
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (21.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 22nd percentile — 21.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Useplunk Plunk — versions < 0.8.0
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/useplunk/plunk/security/advisories/GHSA-2mvm-rg5v-7hfq (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-34975?
- CVE-2026-34975 is a high-severity vulnerability in Useplunk Plunk, classified under CRLF Injection. CVSS score: 8.5/10. Published 2026-04-06.
- How severe is CVE-2026-34975?
- High severity. CVSS v3 base score is 8.5 out of 10.
- Is CVE-2026-34975 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.