PT-2026-36987 · Ruby · Net::Imap

Masamuneee · Published 2026-05-04 · Updated 2026-05-18 · CVE-2026-42256

Positive Technologies (AI Summary)

CVSS v3.1

6.5

Medium

Base vector

AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Name of the Vulnerable Software and Affected Versions net-imap (affected versions not specified)

Description A hostile IMAP server can trigger a computational denial-of-service attack on the client process during authentication using SCRAM-SHA1 or SCRAM-SHA256. By sending an arbitrarily large PBKDF2 iteration count in the server-first-message, the server forces the client to execute an expensive OpenSSL::KDF.pbkdf2 hmac() call. Since this function is a blocking C extension that holds the Ruby Global VM Lock (a mechanism that ensures only one thread executes Ruby code at a time), it can freeze the entire Ruby VM and block all threads for several minutes, depending on the hardware and OpenSSL version.

Recommendations Upgrade to a patched version of net-imap and call Net::IMAP#authenticate using a max iterations keyword argument set to a safe value appropriate for the security context. Avoid using SCRAM-* mechanisms when authenticating to untrusted servers.

Exploit

Fix

DoS

Allocation of Resources Without Limits

Weakness Enumeration

CWE-770

CWE-1322

Related Identifiers

CVE-2026-42256

GHSA-87PF-FPWV-P7M7

Affected Products

Net::Imap

References · 26

• 🔥 https://github.com/rubysec/ruby-advisory-db/blob/master/gems/net-imap/CVE-2026-42256.yml · Exploit
• https://github.com/ruby/net-imap/commit/808001bc45c06f7297a7e96d341279e041a7f7f4 · Patch
• https://github.com/ruby/net-imap/commit/158d0b505074397cdb5ceb58935e42dd2bcfa612 · Patch
• https://github.com/ruby/net-imap/commit/99f59eab6064955a23debd95410263ad144df758 · Patch
• https://github.com/ruby/net-imap/security/advisories/GHSA-87pf-fpwv-p7m7 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2026-42256 · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-87pf-fpwv-p7m7 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-42256 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-42256 · Vendor Advisory
• https://osv.dev/vulnerability/BELL-CVE-2026-42256 · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2026-42256 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-42256 · Security Note
• https://nvd.nist.gov/vuln/detail/CVE-2026-42256 · Security Note
• https://github.com/ruby/net-imap/releases/tag/v0.6.4 · Note
• https://github.com/ruby/net-imap/releases/tag/v0.5.14 · Note