CVE-2025-43857 | net-imap rubygem vulnerable to possible DoS by memory exhaustion

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5, there is a possibility for denial of service by memory exhaustion when net-imap reads server responses. At any time while the client is connected, a malicious server can send can send a "literal" byte count, which is automatically read by the client's receiver thread. The response reader immediately allocates memory for the number of bytes indicated by the server response. This should not be an issue when securely connecting to trusted IMAP servers that are well-behaved. It can affect insecure connections and buggy, untrusted, or compromised servers (for example, connecting to a user supplied hostname). This issue has been patched in versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5.

Published: 2025-04-28 Last update: 2025-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-43857 is rated Moderate Risk (47.7/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.53%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-43857

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-02-22 0.14% 0.53% +0.38%
2 2026-01-22 0.16% 0.14% -0.01%
3 2026-01-01 — 0.16% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-43857

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.0 4.0 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:P)
Additional preconditions must be present for exploitation.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:P)
A user has to participate (for example click/open/approve).
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:H)
High availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:X)
Not evaluated.
Recovery (supplemental) (R:X)
Not evaluated.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:X)
Not evaluated.
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2025-43857

GitHub Security Advisory for CVE-2025-43857

GHSA-j3g3-5qv5-52mj · Severity: medium · Ecosystem: rubygems — net-imap rubygem vulnerable to possible DoS by memory exhaustion

OS Trackers for CVE-2025-43857

vendor priority summary link
alpine — CVE-2025-43857: 1 source package rows (ruby-net-imap); 2 state rows across 2 repos (3.20-main, 3.21-main); fixed 2, open 0. https://security.alpinelinux.org/vuln/CVE-2025-43857
debian not yet assigned CVE-2025-43857 not yet assigned priority: Debian including 2 source packages (ruby3.1, ruby3.3), 4 status rows across 4 suites (bookworm, forky, sid, trixie): open 4. https://security-tracker.debian.org/tracker/CVE-2025-43857
redhat medium — https://access.redhat.com/security/cve/CVE-2025-43857
suse medium CVE-2025-43857 severity moderate: SUSE including 14 source package names (hawk2, libruby2_1-2_1, …), 203 product×package rows across 41 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Linux Enterprise High Availability Extension 12 SP5, … (41 product lines)): Known Not Affected 203. https://www.suse.com/security/cve/CVE-2025-43857/
ubuntu low CVE-2025-43857 low priority: Ubuntu including 7 source packages (jruby, ruby2.3, …), 54 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 31, needs-triage 17, ignored 4, not-affected 2. https://ubuntu.com/security/CVE-2025-43857

Affected software / configurations for CVE-2025-43857

Vendor Product Version Raw CPE
ruby-lang net::imap < 0.2.5 cpe:2.3:a:ruby-lang:net\:\:imap:*:*:*:*:*:ruby:*:*
ruby-lang net::imap >= 0.3.0, < 0.3.9 cpe:2.3:a:ruby-lang:net\:\:imap:*:*:*:*:*:ruby:*:*
ruby-lang net::imap >= 0.4.0, < 0.4.20 cpe:2.3:a:ruby-lang:net\:\:imap:*:*:*:*:*:ruby:*:*
ruby-lang net::imap >= 0.5.0, < 0.5.7 cpe:2.3:a:ruby-lang:net\:\:imap:*:*:*:*:*:ruby:*:*

References for CVE-2025-43857

cvelogic Threat Intelligence