CVE-2026-55200: libssh2 Integer Overflow to Buffer Overflow
Vulnerability summary
CVE-2026-55200 is a critical (CVSS 9.2) Integer Overflow to Buffer Overflow vulnerability in libssh2. EPSS estimates a 4.02% chance of exploitation in the next 30 days, higher than 90.4% of scored vulnerabilities. 1 public exploit is recorded.
Advisory lineage
Upstream 0 · Downstream 6 · Related 7Timeline
- 17-06-2026PublishedVulnerability first disclosed.
- 14-07-2026Last modifiedVulnerability information updated.
Description
libssh2 through 1.11.1, fixed in commit 7acf3df contains an out-of-bounds write vulnerability in ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote code execution.
CVSS metrics
10 scores · 7 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated9.2CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · WolfiEcosystem advisory · calculated9.2CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated9.2CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- NVDNIST9.2CriticalCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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
- OSV · AlpineEcosystem advisory · calculated8.3HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:LDiffers
- OSV · UbuntuEcosystem advisory · calculated8.3HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:LDiffers
- OSV · DebianEcosystem advisory · calculated8.3HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:LDiffers
- NVDNIST8.3HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:LDiffers
EPSS trend
Probability
4.02%
Chance of exploitation in the next 30 days
Percentile
90%
Versus all other CVEs
30-day change
0.00 pp
From 4.02% on 20-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
1 foundExploitarium
Maturity: poc
Weaknesses
CWE · root causeAffected systems
Chainguard3 products
- libssh2< 1.11.1-r6
- libssh2-dev< 1.11.1-r6
- libssh2-doc< 1.11.1-r6
Wolfi3 products
- libssh2< 1.11.1-r6
- libssh2-dev< 1.11.1-r6
- libssh2-doc< 1.11.1-r6
Alpine2 products
- libssh2< 1.11.1-r2 | < 1.11.1-r3
- rust< 1.96.1-r0
Debian1 product
- libssh2< 1.11.1-1+deb13u1 | < 1.11.1-4
Libssh21 product
- libssh2≤ 1.11.1 | 1.11.1
Ubuntu1 product
- libssh2< 1.11.1-1ubuntu0.25.10.2 | < 1.11.1-1ubuntu0.26.04.2
6 vendors · 11 products
References
12 links- www.vulncheck.com/advisories/libssh2-out-of-bounds-write-via-unchecked-packet-length-in-transport-cThird Party AdvisoryAdvisory
Show all 12 references
- github.com/libssh2/libssh2PACKAGE