CVE-2015-6525: Multiple integer overflows in the evbuffer API in Libevent 2.0.x before 2.0.22 and 2.1.x before 2.1.5-beta all

This month

HIGH 7.5WATCHLISTMITIGATEDOWNGRADE

CVE-2015-6525 is a high-severity flaw (CVSS 7.5) affecting debian linux, libevent. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Multiple integer overflows in the evbuffer API in Libevent 2.0.x before 2.0.22 and 2.1.x before 2.1.5-beta allow context-dependent attackers to cause a denial of service or possibly have other unspecified impact via "insanely large inputs" to the (1) evbuffer_add, (2) evbuffer_prepend, (3) evbuffer_expand, (4) exbuffer_reserve_space, or (5) evbuffer_read function, which triggers a heap-based buffer overflow or an infinite loop. NOTE: this identi

Why this priority

High severity
EPSS top 8%: very likely to be exploited
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
EPSS exploit chance	4.8% (top 8%)
CISA exploited list	No
Weakness	CWE-189
Published	2015-08-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · libevent project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2015-08-24 14:59 UTCPublished CVE record published
2026-06-17 00:31 UTCUpdated Record last modified

debian debian linux MITIGATE

Affected: 7.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

libevent project libevent DOWNGRADE

Affected: 2.0.1 · 2.0.2 · 2.0.3 · 2.0.4 · 2.0.5 · 2.0.6 · 2.0.7 · 2.0.8

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.0.1

1. Check installed version

apt-cache policy libevent || rpm -q libevent || libevent --version

2. No fixed release: DOWNGRADE to a release before 2.0.1 (Debian / Ubuntu)

apt-cache madison libevent sudo apt install libevent=<VERSION_BEFORE_2.0.1> sudo apt-mark hold libevent

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libevent sudo dnf downgrade libevent-<VERSION_BEFORE_2.0.1> sudo dnf versionlock add libevent

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2015-6525?

debian linux: mitigate or apply the listed mitigation; libevent: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2015-6525 being exploited?

CVE-2015-6525 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2015-6525 affect?

CVE-2015-6525 affects debian linux, libevent. Severity is high (CVSS 7.5). Multiple integer overflows in the evbuffer API in Libevent 2.0.x before 2.0.22 and 2.1.x before 2.1.5-beta allow context-dependent attackers to cause a denial of service or possibly have other unspecified impact via "insanely large inputs"

How urgent is CVE-2015-6525?

Priority 54/100. High severity; EPSS top 8%: very likely to be exploited; On your watchlist

Software pages

Debian vulnerabilities

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References

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