Staging Environment: Content and features may be unstable or change without notice.
Advisory details: github_osv / GHSA-8x48-8g7j-rqxp
Advisory ID github_osv/GHSA-8x48-8g7j-rqxp
Aliases
Summary Duplicate Advisory: Quadratic-time DoS in PorterStemmer via long runs of 'y' ## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-ww6m-cw3f-q94g. This link is maintained to preserve external references. ## Original Description nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter 'y' followed by a matching suffix (e.g., 'ness') can pin a CPU core for seconds to minutes, causing availability impact.
Status Published
Exploitability 0.5
Weighted Severity 7.8
Risk 3.9
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (1)
CWE-407 Inefficient Algorithmic Complexity
System Score Found at
cvssv3.1 7.5 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-8x48-8g7j-rqxp/GHSA-8x48-8g7j-rqxp.json
cvssv4 8.7 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-8x48-8g7j-rqxp/GHSA-8x48-8g7j-rqxp.json
generic_textual HIGH
Reference id Reference type URL
https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g
https://www.vulncheck.com/advisories/nltk-porterstemmer-before-3.10.3-quadratic-time-dos
CVE-2026-81722 https://nvd.nist.gov/vuln/detail/CVE-2026-81722
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-8x48-8g7j-rqxp/GHSA-8x48-8g7j-rqxp.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/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 Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-8x48-8g7j-rqxp/GHSA-8x48-8g7j-rqxp.json
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.