CVE-2017-9847: The bdecode function in bdecode.cpp in libtorrent 1.1.3 allows remote attackers to cause a denial of service (

Routine

MEDIUM 5.5DOWNGRADE

CVE-2017-9847 is a medium-severity flaw (CVSS 5.5) affecting libtorrent. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The bdecode function in bdecode.cpp in libtorrent 1.1.3 allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) via a crafted file.

Why this priority

No elevated risk signals yet

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

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.1% (top 35%)
CISA exploited list	No
Weakness	CWE-125
Published	2017-06-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: libtorrent

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

Am I affected?

Timeline

2017-06-24 17:29 UTCPublished CVE record published
2026-06-17 01:29 UTCUpdated Record last modified

libtorrent libtorrent DOWNGRADE

Affected: 1.1.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.1.3

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.1.3 (Debian / Ubuntu)

apt-cache madison libtorrent sudo apt install libtorrent=<VERSION_BEFORE_1.1.3> sudo apt-mark hold libtorrent

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

dnf --showduplicates list libtorrent sudo dnf downgrade libtorrent-<VERSION_BEFORE_1.1.3> sudo dnf versionlock add libtorrent

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-2017-9847?

libtorrent: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2017-9847 being exploited?

CVE-2017-9847 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-2017-9847 affect?

CVE-2017-9847 affects libtorrent. Severity is medium (CVSS 5.5). The bdecode function in bdecode.cpp in libtorrent 1.1.3 allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) via a crafted file.

How urgent is CVE-2017-9847?

Priority 35/100. No elevated risk signals yet.

Related CVEs

CVE-2016-7164 HIGH 7.5 DOWNGRADE The construct function in puff.cpp in Libtorrent 1.1.0 allows remote torrent trackers to cause a denial of ser
CVE-2016-5301 HIGH 7.5 MITIGATE MITIGATE The parse_chunk_header function in libtorrent before 1.1.1 allows remote attackers to cause a denial of servic

References

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