CVE-2025-31498 | c-ares has a use-after-free in read_answers()

c-ares is an asynchronous resolver library. From 1.32.3 through 1.34.4, there is a use-after-free in read_answers() when process_answer() may re-enqueue a query either due to a DNS Cookie Failure or when the upstream server does not properly support EDNS, or possibly on TCP queries if the remote closed the connection immediately after a response. If there was an issue trying to put that new transaction on the wire, it would close the connection handle, but read_answers() was still expecting the connection handle to be available to possibly dequeue other responses. In theory a remote attacker might be able to trigger this by flooding the target with ICMP UNREACHABLE packets if they also control the upstream nameserver and can return a result with one of those conditions, this has been untested. Otherwise only a local attacker might be able to change system behavior to make send()/write() return a failure condition. This vulnerability is fixed in 1.34.5.

Published: 2025-04-08 Last update: 2026-04-15 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-31498 is rated Moderate Risk (58.1/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.65%). 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-2025-31498

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 2026-05-17 0.62% 0.65% +0.03%
2 2026-04-13 0.67% 0.62% -0.05%
3 2026-04-10 — 0.67% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-31498

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.3 4.0 HIGH
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/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:H)
Exploitation depends on constrained or hard-to-reproduce conditions.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:L)
Limited 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]

Weakness enumeration for CVE-2025-31498

OS Trackers for CVE-2025-31498

vendor priority summary link
alpine high CVE-2025-31498: 1 source package rows (c-ares); 7 state rows across 4 repos (3.20-main, 3.21-main, 3.22-main, edge-main); fixed 3, open 4. https://security.alpinelinux.org/vuln/CVE-2025-31498
debian unimportant CVE-2025-31498 unimportant priority: Debian including 1 source packages (c-ares), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-31498
redhat medium — https://access.redhat.com/security/cve/CVE-2025-31498
suse medium CVE-2025-31498 severity moderate: SUSE including 32 source package names (c-ares, c-ares-devel, …), 99 product×package rows across 31 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Liberty Linux 8, … (31 product lines)): Known Not Affected 72, Fixed 27. https://www.suse.com/security/cve/CVE-2025-31498/
ubuntu medium CVE-2025-31498 medium priority: Ubuntu including 1 source packages (c-ares), 8 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, upstream, xenial): not-affected 5, released 3. https://ubuntu.com/security/CVE-2025-31498

Affected software / configurations for CVE-2025-31498

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-31498

cvelogic Threat Intelligence